diff --git a/crates/engine/src/cmd/effectcmd.rs b/crates/engine/src/cmd/effectcmd.rs
index abffe675c..c9ebf4214 100644
--- a/crates/engine/src/cmd/effectcmd.rs
+++ b/crates/engine/src/cmd/effectcmd.rs
@@ -138,6 +138,7 @@ pub(crate) fn apply(s: &mut Session, p: &Value) -> Result<Value> {
     if !params.is_null() && !params.is_object() {
         return Err(bad(C, "`params` must be an object"));
     }
+    super::params::check_effect_color(C, id, &params)?;
     // Crop Marks take their style from the preferences when applied.
     if id == effects::CROP_MARKS && params.get("style").is_none() {
         params["style"] = json!(s.crop_mark_style().id());
@@ -313,7 +314,11 @@ fn set_params(s: &mut Session, p: &Value) -> Result<Value> {
         .transpose()?;
     let visible = p.get("visible").and_then(Value::as_bool);
     let item = item_target(s, p, C)?;
-    if set_params_effects(s, p).iter().any(|e| e == GLASS) {
+    let edited = set_params_effects(s, p);
+    for effect in &edited {
+        super::params::check_effect_color(C, effect, &params)?;
+    }
+    if edited.iter().any(|e| e == GLASS) {
         load_texture(&mut params, C)?;
     }
     for id in appearance_targets(s, p)? {
diff --git a/crates/engine/src/cmd/params.rs b/crates/engine/src/cmd/params.rs
index 7989071f0..5d70a9fa5 100644
--- a/crates/engine/src/cmd/params.rs
+++ b/crates/engine/src/cmd/params.rs
@@ -13,7 +13,9 @@
 //! command with its default. So are the `params` of an effect (#1592): `effect.apply` and
 //! `effect.setParams` answer a key the effect doesn't take, or a value of another type than its
 //! default, with a parameter error ([`check_effect_params`]). [`Session::execute`] itself takes
-//! what it is given, so the journal of an older version still replays.
+//! what it is given, so the journal of an older version still replays, except for an effect's
+//! `color` that the effect can't read, which `effect.apply` and `effect.setParams` refuse
+//! themselves ([`check_effect_color`]).
 
 use serde_json::Value;
 
@@ -212,8 +214,9 @@ fn unknown(id: &str, key: &str, keys: &[&str]) -> crate::EngineError {
 
 /// `params` of built-in effect `effect`, as command `id` was given them (#1592): only keys the
 /// effect takes (those of its dialog defaults and of its params description), each of its
-/// default's type. Numbers out of range pass: the effect clamps them when it draws. An effect
-/// plug-in resolves its own against its manifest, and an unknown effect is the command's to report.
+/// default's type, and a `color` the effect can draw ([`check_effect_color`]). Numbers out of
+/// range pass: the effect clamps them when it draws. An effect plug-in resolves its own against
+/// its manifest, and an unknown effect is the command's to report.
 pub fn check_effect_params(id: &str, effect: &str, params: &Value) -> Result<()> {
     let Value::Object(given) = params else { return Ok(()) };
     if effect.starts_with(vectorcraft_plugins::effect::PREFIX) {
@@ -240,6 +243,40 @@ pub fn check_effect_params(id: &str, effect: &str, params: &Value) -> Result<()>
             _ => {}
         }
     }
+    check_effect_color(id, effect, params)
+}
+
+/// Can an effect read `v` as its `color`: a string [`Color::from_hex`] reads (`#rrggbb`, `#rgb`,
+/// `#rrggbbaa`, black, white, red, green, blue), `[r, g, b]` whose first three entries are numbers
+/// (read on a 0..1 scale) or a color object (`{"model": "rgb", "r": …}`)? The effect draws its
+/// default color for any other value, except that an array of three or more entries draws an
+/// entry that isn't a number as 0.
+///
+/// [`Color::from_hex`]: vectorcraft_color::Color::from_hex
+fn is_effect_color(v: &Value) -> bool {
+    match v {
+        Value::String(s) => vectorcraft_color::Color::from_hex(s).is_some(),
+        Value::Array(a) => a.len() >= 3 && a.iter().take(3).all(Value::is_number),
+        Value::Object(_) => serde_json::from_value::<vectorcraft_color::Color>(v.clone()).is_ok(),
+        _ => false,
+    }
+}
+
+/// The `color` in `params` of built-in effect `effect`, when the effect has a `color` parameter,
+/// as command `id` was given it: a parameter error naming it unless the effect can read it
+/// ([`is_effect_color`]). `effect.apply` and `effect.setParams` run this themselves before they
+/// edit, so the app's own edits, the steps of a `command.batch` and a replayed journal are held to
+/// it too.
+pub(crate) fn check_effect_color(id: &str, effect: &str, params: &Value) -> Result<()> {
+    let key = "color";
+    let Some(v) = params.get(key) else { return Ok(()) };
+    if effect.starts_with(vectorcraft_plugins::effect::PREFIX) {
+        return Ok(());
+    }
+    let takes_color = vectorcraft_render::effects::effect_info(effect).is_some_and(|info| info.defaults.get(key).is_some_and(Value::is_string));
+    if takes_color && !is_effect_color(v) {
+        return Err(bad(id, format!("`{key}` must be a #rrggbb color")));
+    }
     Ok(())
 }
 
diff --git a/crates/engine/tests/param_keys.rs b/crates/engine/tests/param_keys.rs
index cc0551e8f..b8e00bea6 100644
--- a/crates/engine/tests/param_keys.rs
+++ b/crates/engine/tests/param_keys.rs
@@ -44,6 +44,58 @@ fn effect_params_no_longer_taken_still_replay_and_open() {
     assert_eq!(stored(&back)["blurr"], json!(3));
 }
 
+/// An effect's `color` that the effect can't read (a string `Color::from_hex` doesn't read, an
+/// `[r, g, b]` without three numbers, an object that isn't a color, `null`) is refused by
+/// `effect.apply`, `appearance.addEffect` and `effect.setParams` themselves, not only by the check,
+/// and the document and its undo history stay as they were. The forms the effect reads pass. A
+/// document saved with an unreadable color still opens with it.
+#[test]
+fn an_effect_color_it_cannot_draw_is_refused() {
+    let mut s = Session::new();
+    s.execute("file.new", &json!({})).unwrap();
+    let id = s.execute("shape.rectangle", &json!({"x": 10, "y": 10, "width": 50, "height": 40})).unwrap()["id"].as_u64().unwrap();
+    s.execute("effect.apply", &json!({"effect": "stylize.dropShadow", "params": {"color": "#ff0000"}})).unwrap();
+    let state = |s: &Session| {
+        let st = s.active().unwrap();
+        (st.doc.clone(), st.history.undo.len())
+    };
+    let before = state(&s);
+    let why = "`color` must be a #rrggbb color";
+    for bad in [json!("not-a-color"), json!("#ff00"), json!([1, 0]), json!(["#ff0000", 0, 0]), json!({"gray": 50}), json!(null)] {
+        for (cmd, params) in [
+            ("effect.setParams", json!({"index": 0, "params": {"color": bad}})),
+            ("effect.apply", json!({"effect": "stylize.outerGlow", "params": {"color": bad}})),
+            ("appearance.addEffect", json!({"effect": "adjust.shiftToColor", "params": {"color": bad}})),
+        ] {
+            let e = s.execute(cmd, &params).unwrap_err().to_string();
+            assert!(e.contains(why), "{cmd} {params}: {e}");
+            let checked = s.check_params(cmd, &params).unwrap_err().to_string();
+            assert!(checked.contains(why), "{cmd} {params}: {checked}");
+            assert!(state(&s) == before, "{cmd} {params} changed the document or its undo history");
+        }
+    }
+    let stored = |s: &Session| s.active().unwrap().doc.layers[0].children().unwrap()[0].appearance.effects[0].params["color"].clone();
+    for good in [
+        json!("#00ff00"),
+        json!("#0f0"),
+        json!("00ff00"),
+        json!("#00ff00ff"),
+        json!("green"),
+        json!([0, 1, 0]),
+        json!({"model": "rgb", "r": 0.0, "g": 1.0, "b": 0.0}),
+        json!({"model": "cmyk", "c": 1.0, "m": 0.0, "y": 1.0, "k": 0.0}),
+    ] {
+        let params = json!({"index": 0, "params": {"color": good}});
+        s.check_params("effect.setParams", &params).unwrap_or_else(|e| panic!("{good}: {e}"));
+        s.execute("effect.setParams", &params).unwrap_or_else(|e| panic!("{good}: {e}"));
+        assert_eq!(stored(&s), good);
+    }
+    let mut doc = (*s.active().unwrap().doc).clone();
+    doc.node_mut(vectorcraft_doc::NodeId(id)).unwrap().appearance.effects[0].params["color"] = json!("not-a-color");
+    let back = vectorcraft_format::load(&vectorcraft_format::save(&doc, false)).unwrap();
+    assert_eq!(back.layers[0].children().unwrap()[0].appearance.effects[0].params["color"], json!("not-a-color"));
+}
+
 /// What a command adds to its own journal entry passes the check, so a recorded journal can be
 /// sent back through the control channel or MCP.
 #[test]
diff --git a/crates/ui-egui/src/dialogs/effect.rs b/crates/ui-egui/src/dialogs/effect.rs
index 669532ef2..95fdabd23 100644
--- a/crates/ui-egui/src/dialogs/effect.rs
+++ b/crates/ui-egui/src/dialogs/effect.rs
@@ -604,26 +604,14 @@ fn command(d: &Dialog) -> (&'static str, Value) {
 
 fn confirm(app: &mut VectorcraftApp, d: &Dialog) -> Result<Value, String> {
     let (cmd, p) = command(d);
-    if super::warp_effect::is_warp(&d.str("__effect")) {
-        let r = form::commit_preview(app, cmd, p.clone())?;
-        if cmd == "effect.apply" {
-            app.last_effect = Some((d.str("__effect"), p["params"].clone()));
-        }
-        return Ok(r);
-    }
-    let r = if app.session.in_interaction() {
-        // Live preview already applied: keep it (the interaction commits as one undo step).
-        let _ = app.session.preview(cmd, &p);
-        app.session.commit_interaction().map(|_| Value::Null).map_err(|e| e.to_string())
-    } else {
-        app.run(cmd, p.clone())
-    };
+    // A live preview commits as one undo step. When the command refuses the values (a Color the
+    // effect can't draw), the dialog stays open and the error is returned.
+    let r = form::commit_preview(app, cmd, p.clone())?;
     // Last Effect repeats applied effects, not edits.
     if cmd == "effect.apply" {
         app.last_effect = Some((d.str("__effect"), p["params"].clone()));
     }
-    app.ui.dialog = None;
-    r
+    Ok(r)
 }
 
 #[cfg(test)]
diff --git a/crates/ui-egui/src/dialogs/tests.rs b/crates/ui-egui/src/dialogs/tests.rs
index 18dbd2b3c..32ff56b2b 100644
--- a/crates/ui-egui/src/dialogs/tests.rs
+++ b/crates/ui-egui/src/dialogs/tests.rs
@@ -174,6 +174,27 @@ fn effect_preview_is_kept_as_one_undo_step() {
     assert_eq!(app.session.doc().unwrap().doc, before);
 }
 
+/// Drop Shadow's Color typed as text the effect can't draw: OK returns the error and keeps the
+/// dialog open, with Preview on or off, and the document stays as it was.
+#[test]
+fn effect_dialog_refuses_a_color_it_cannot_draw() {
+    for preview in [true, false] {
+        let mut app = app();
+        app.run("shape.rectangle", json!({"x": 10, "y": 10, "width": 50, "height": 50})).unwrap();
+        app.run("select.all", json!({})).unwrap();
+        let before = app.session.doc().unwrap().doc.clone();
+        app.run("effect.dialog", json!({"effect": "stylize.dropShadow"})).unwrap();
+        let d = app.ui.dialog.as_mut().unwrap();
+        d.fields.insert("preview".into(), json!(preview));
+        d.fields.insert("color".into(), json!("not-a-color"));
+        frame(&mut app, Default::default());
+        let e = confirm(&mut app).unwrap_err();
+        assert!(e.contains("`color` must be a #rrggbb color"), "preview {preview}: {e}");
+        assert!(app.ui.dialog.is_some() && app.last_effect.is_none(), "preview {preview}");
+        assert_eq!(app.session.doc().unwrap().doc, before, "preview {preview}");
+    }
+}
+
 #[test]
 fn raster_filter_dialogs_preview_and_apply() {
     for (effect, key, value) in [
diff --git a/crates/ui-egui/src/i18n/bg.tsv b/crates/ui-egui/src/i18n/bg.tsv
index 5f93a3fd1..fe4f3457c 100644
--- a/crates/ui-egui/src/i18n/bg.tsv
+++ b/crates/ui-egui/src/i18n/bg.tsv
@@ -3605,6 +3605,7 @@ axis	Both	И двете
 @msg	`{id}` has no envelope dialog	`{id}` няма диалогов прозорец за обвивка
 @msg	`{keep}` is not a side of this axis	`{keep}` не е страна на тази ос
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` трябва да бъде `auto` или езиков код като `en` или `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` трябва да бъде цвят във формат #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` трябва да бъде цвят във формат #rrggbb
 @msg	`{key}` must be a number	`{key}` трябва да бъде число
 @msg	`{key}` must be a string	`{key}` трябва да бъде низ
diff --git a/crates/ui-egui/src/i18n/cs.tsv b/crates/ui-egui/src/i18n/cs.tsv
index 6ca2a3d9c..42decb52a 100644
--- a/crates/ui-egui/src/i18n/cs.tsv
+++ b/crates/ui-egui/src/i18n/cs.tsv
@@ -3976,6 +3976,7 @@ imageTrace	Outline	Obrys
 @msg	`{id}` has no envelope dialog	`{id}` nemá dialogové okno obálky
 @msg	`{keep}` is not a side of this axis	`{keep}` není strana této osy
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` musí být `auto` nebo kód jazyka, například `en` nebo `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` musí být barva #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` musí být barva #rrggbb
 @msg	`{key}` must be a number	`{key}` musí být číslo
 @msg	`{key}` must be a string	`{key}` musí být řetězec
diff --git a/crates/ui-egui/src/i18n/de.tsv b/crates/ui-egui/src/i18n/de.tsv
index 9f7ee9465..e0aeefc7a 100644
--- a/crates/ui-egui/src/i18n/de.tsv
+++ b/crates/ui-egui/src/i18n/de.tsv
@@ -3579,6 +3579,7 @@ theme	Appearance	Erscheinungsbild
 @msg	`{id}` has no envelope dialog	`{id}` hat kein Hüllendialogfeld
 @msg	`{keep}` is not a side of this axis	`{keep}` ist keine Seite dieser Achse
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` muss `auto` oder ein Sprachcode wie `en` oder `zh-hant` sein
+@msg	`{key}` must be a #rrggbb color	`{key}` muss eine Farbe der Form #rrggbb sein
 @msg	`{key}` must be a #rrggbb colour	`{key}` muss eine Farbe der Form #rrggbb sein
 @msg	`{key}` must be a number	`{key}` muss eine Zahl sein
 @msg	`{key}` must be a string	`{key}` muss eine Zeichenfolge sein
diff --git a/crates/ui-egui/src/i18n/el.tsv b/crates/ui-egui/src/i18n/el.tsv
index 66977f54d..77168a212 100644
--- a/crates/ui-egui/src/i18n/el.tsv
+++ b/crates/ui-egui/src/i18n/el.tsv
@@ -1988,6 +1988,7 @@ axis	Both	Και τα δύο
 @msg	`{id}` has no envelope dialog	Το `{id}` δεν έχει παράθυρο διαλόγου περιβλήματος
 @msg	`{keep}` is not a side of this axis	Το `{keep}` δεν είναι πλευρά αυτού του άξονα
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	Το `{key}` πρέπει να είναι `auto` ή κωδικός γλώσσας όπως `en` ή `zh-hant`
+@msg	`{key}` must be a #rrggbb color	Το `{key}` πρέπει να είναι χρώμα #rrggbb
 @msg	`{key}` must be a #rrggbb colour	Το `{key}` πρέπει να είναι χρώμα #rrggbb
 @msg	`{key}` must be a number	Το `{key}` πρέπει να είναι αριθμός
 @msg	`{key}` must be a string	Το `{key}` πρέπει να είναι συμβολοσειρά
diff --git a/crates/ui-egui/src/i18n/es.tsv b/crates/ui-egui/src/i18n/es.tsv
index 1067afa8b..631f92491 100644
--- a/crates/ui-egui/src/i18n/es.tsv
+++ b/crates/ui-egui/src/i18n/es.tsv
@@ -3676,6 +3676,7 @@ axis	Both	Ambos
 @msg	`{id}` has no envelope dialog	`{id}` no tiene cuadro de diálogo de envolvente
 @msg	`{keep}` is not a side of this axis	`{keep}` no es un lado de este eje
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` debe ser `auto` o un código de idioma como `en` o `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` debe ser un color #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` debe ser un color #rrggbb
 @msg	`{key}` must be a number	`{key}` debe ser un número
 @msg	`{key}` must be a string	`{key}` debe ser un texto
diff --git a/crates/ui-egui/src/i18n/fi.tsv b/crates/ui-egui/src/i18n/fi.tsv
index c357563e5..a2a954356 100644
--- a/crates/ui-egui/src/i18n/fi.tsv
+++ b/crates/ui-egui/src/i18n/fi.tsv
@@ -3903,6 +3903,7 @@ imageTrace	Outline	Ääriviiva
 @msg	`{id}` has no envelope dialog	`{id}`: ei vääristyskuoren valintaikkunaa
 @msg	`{keep}` is not a side of this axis	`{keep}` ei ole tämän akselin puoli
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` on oltava `auto` tai kielikoodi, kuten `en` tai `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` on oltava #rrggbb-väri
 @msg	`{key}` must be a #rrggbb colour	`{key}` on oltava #rrggbb-väri
 @msg	`{key}` must be a number	`{key}` on oltava luku
 @msg	`{key}` must be a string	`{key}` on oltava merkkijono
diff --git a/crates/ui-egui/src/i18n/fr.tsv b/crates/ui-egui/src/i18n/fr.tsv
index e74016c88..536305f24 100644
--- a/crates/ui-egui/src/i18n/fr.tsv
+++ b/crates/ui-egui/src/i18n/fr.tsv
@@ -3673,6 +3673,7 @@ axis	Both	Les deux
 @msg	`{id}` has no envelope dialog	`{id}` n’a pas de boîte de dialogue d’enveloppe
 @msg	`{keep}` is not a side of this axis	`{keep}` n’est pas un côté de cet axe
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` doit être `auto` ou un code de langue comme `en` ou `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` doit être une couleur #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` doit être une couleur #rrggbb
 @msg	`{key}` must be a number	`{key}` doit être un nombre
 @msg	`{key}` must be a string	`{key}` doit être une chaîne
diff --git a/crates/ui-egui/src/i18n/hu.tsv b/crates/ui-egui/src/i18n/hu.tsv
index 8e28c70a6..bbf81ef0d 100644
--- a/crates/ui-egui/src/i18n/hu.tsv
+++ b/crates/ui-egui/src/i18n/hu.tsv
@@ -4169,6 +4169,7 @@ imageTrace	Outline	Körvonal
 @msg	`{id}` has no envelope dialog	ennek nincs burkoló-párbeszédablaka: `{id}`
 @msg	`{keep}` is not a side of this axis	`{keep}` nem ennek a tengelynek az oldala
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}`: `auto` vagy nyelvkód kell, például `en` vagy `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}`: #rrggbb szín kell
 @msg	`{key}` must be a #rrggbb colour	`{key}`: #rrggbb szín kell
 @msg	`{key}` must be a number	`{key}`: szám kell
 @msg	`{key}` must be a string	`{key}`: szöveg kell
diff --git a/crates/ui-egui/src/i18n/it.tsv b/crates/ui-egui/src/i18n/it.tsv
index e781a57e6..5923a3518 100644
--- a/crates/ui-egui/src/i18n/it.tsv
+++ b/crates/ui-egui/src/i18n/it.tsv
@@ -3679,6 +3679,7 @@ axis	Both	Entrambi
 @msg	`{id}` has no envelope dialog	`{id}` non ha una finestra di dialogo per l'involucro
 @msg	`{keep}` is not a side of this axis	`{keep}` non è un lato di questo asse
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` deve essere `auto` o un codice lingua come `en` o `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` deve essere un colore #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` deve essere un colore #rrggbb
 @msg	`{key}` must be a number	`{key}` deve essere un numero
 @msg	`{key}` must be a string	`{key}` deve essere una stringa
diff --git a/crates/ui-egui/src/i18n/ja.tsv b/crates/ui-egui/src/i18n/ja.tsv
index e925da051..52e746d9e 100644
--- a/crates/ui-egui/src/i18n/ja.tsv
+++ b/crates/ui-egui/src/i18n/ja.tsv
@@ -3857,6 +3857,7 @@ swatch	Bright Violet	ビビッドバイオレット
 @msg	no artboard	アートボードがありません
 @msg	installing from a path is not available on the web; pass the module as `dataBase64`	Web 版ではファイルパスからはインストールできないため、モジュールは `dataBase64` で渡してください
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` は `auto` か、`en` や `zh-hant` などの言語コードにしてください
+@msg	`{key}` must be a #rrggbb color	`{key}` は #rrggbb 形式のカラーにしてください
 @msg	`{key}` must be a #rrggbb colour	`{key}` は #rrggbb 形式のカラーにしてください
 @msg	`{key}` must be a string	`{key}` は文字列にしてください
 @msg	`{key}` must be a whole number	`{key}` は整数にしてください
diff --git a/crates/ui-egui/src/i18n/ko.tsv b/crates/ui-egui/src/i18n/ko.tsv
index c22818da9..6b1c35f4c 100644
--- a/crates/ui-egui/src/i18n/ko.tsv
+++ b/crates/ui-egui/src/i18n/ko.tsv
@@ -3789,6 +3789,7 @@ theme	Appearance	외관
 @msg	no artboard	아트보드가 없습니다
 @msg	installing from a path is not available on the web; pass the module as `dataBase64`	웹에서는 경로로 설치할 수 없습니다. 모듈을 `dataBase64`로 전달하세요
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}`은(는) `auto` 또는 `en`, `zh-hant` 같은 언어 코드여야 합니다
+@msg	`{key}` must be a #rrggbb color	`{key}`은(는) #rrggbb 색상이어야 합니다
 @msg	`{key}` must be a #rrggbb colour	`{key}`은(는) #rrggbb 색상이어야 합니다
 @msg	`{key}` must be a string	`{key}`은(는) 문자열이어야 합니다
 @msg	`{key}` must be a whole number	`{key}`은(는) 정수여야 합니다
diff --git a/crates/ui-egui/src/i18n/pl.tsv b/crates/ui-egui/src/i18n/pl.tsv
index 42801725d..412463bf0 100644
--- a/crates/ui-egui/src/i18n/pl.tsv
+++ b/crates/ui-egui/src/i18n/pl.tsv
@@ -3791,6 +3791,7 @@ imageTrace	Outline	Kontur
 @msg	`{id}` has no envelope dialog	`{id}` nie ma okna dialogowego koperty
 @msg	`{keep}` is not a side of this axis	`{keep}` nie jest stroną tej osi
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` musi mieć wartość `auto` lub kod języka, np. `en` albo `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` musi być kolorem #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` musi być kolorem #rrggbb
 @msg	`{key}` must be a number	`{key}` musi być liczbą
 @msg	`{key}` must be a string	`{key}` musi być ciągiem znaków
diff --git a/crates/ui-egui/src/i18n/pt-br.tsv b/crates/ui-egui/src/i18n/pt-br.tsv
index ea126556b..6b4bbca09 100644
--- a/crates/ui-egui/src/i18n/pt-br.tsv
+++ b/crates/ui-egui/src/i18n/pt-br.tsv
@@ -3275,6 +3275,7 @@ axis	Both	Ambos
 @msg	`{id}` has no envelope dialog	`{id}` não tem caixa de diálogo de envelope
 @msg	`{keep}` is not a side of this axis	`{keep}` não é um lado deste eixo
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` deve ser `auto` ou um código de idioma como `en` ou `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` deve ser uma cor #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` deve ser uma cor #rrggbb
 @msg	`{key}` must be a number	`{key}` deve ser um número
 @msg	`{key}` must be a string	`{key}` deve ser uma string
diff --git a/crates/ui-egui/src/i18n/ru.tsv b/crates/ui-egui/src/i18n/ru.tsv
index c9c9a4055..a6586cc69 100644
--- a/crates/ui-egui/src/i18n/ru.tsv
+++ b/crates/ui-egui/src/i18n/ru.tsv
@@ -3675,6 +3675,7 @@ axis	Both	Оба
 @msg	`{id}` has no envelope dialog	`{id}` не имеет диалогового окна оболочки
 @msg	`{keep}` is not a side of this axis	`{keep}` не является стороной этой оси
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` должно быть `auto` или кодом языка, например `en` или `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` должно быть цветом #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` должно быть цветом #rrggbb
 @msg	`{key}` must be a number	`{key}` должно быть числом
 @msg	`{key}` must be a string	`{key}` должно быть строкой
diff --git a/crates/ui-egui/src/i18n/sv.tsv b/crates/ui-egui/src/i18n/sv.tsv
index f182c945a..b52320ed5 100644
--- a/crates/ui-egui/src/i18n/sv.tsv
+++ b/crates/ui-egui/src/i18n/sv.tsv
@@ -3605,6 +3605,7 @@ axis	Both	Båda
 @msg	`{id}` has no envelope dialog	`{id}` har ingen dialogruta för kuvert
 @msg	`{keep}` is not a side of this axis	`{keep}` är inte en sida av den här axeln
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` måste vara `auto` eller en språkkod som `en` eller `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` måste vara en färg i formatet #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` måste vara en färg i formatet #rrggbb
 @msg	`{key}` must be a number	`{key}` måste vara ett tal
 @msg	`{key}` must be a string	`{key}` måste vara en sträng
diff --git a/crates/ui-egui/src/i18n/tests.rs b/crates/ui-egui/src/i18n/tests.rs
index a17831fbe..c06c193ff 100644
--- a/crates/ui-egui/src/i18n/tests.rs
+++ b/crates/ui-egui/src/i18n/tests.rs
@@ -1251,6 +1251,20 @@ fn unknown_parameter_errors_are_translated() {
     }
 }
 
+/// The error for an effect `color` the effect can't draw, whose text the scan above doesn't read,
+/// is translated whole in each language of [`COMPLETE_MESSAGES`] and in Bulgarian.
+#[test]
+fn effect_color_param_error_is_translated() {
+    use serde_json::json;
+    let p = json!({"effect": "stylize.dropShadow", "params": {"color": "not-a-color"}});
+    let e = vectorcraft_engine::check_params("effect.apply", &p).unwrap_err();
+    let vectorcraft_engine::EngineError::BadParams { msg, .. } = &e else { panic!("{e}") };
+    for code in COMPLETE_MESSAGES.iter().chain(&["bg"]) {
+        let shown = message(Lang::from_code(code).unwrap(), &e.to_string());
+        assert!(!shown.contains(msg.as_str()) && shown.contains("`color`") && shown.contains("effect.apply"), "{code}: {shown}");
+    }
+}
+
 /// The notes of an EPS or `.ai` whose layers weren't read, which the importer pushes as warnings
 /// (the scan above doesn't read them), are translated whole, reason included, as the status bar
 /// shows them after opening (#2035).
diff --git a/crates/ui-egui/src/i18n/uk.tsv b/crates/ui-egui/src/i18n/uk.tsv
index a5299733a..668669767 100644
--- a/crates/ui-egui/src/i18n/uk.tsv
+++ b/crates/ui-egui/src/i18n/uk.tsv
@@ -3663,6 +3663,7 @@ axis	Both	Обидві
 @msg	`{id}` has no envelope dialog	`{id}` не має діалогового вікна оболонки
 @msg	`{keep}` is not a side of this axis	`{keep}` не є стороною цієї осі
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` має бути `auto` або кодом мови, наприклад `en` або `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` має бути кольором #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` має бути кольором #rrggbb
 @msg	`{key}` must be a number	`{key}` має бути числом
 @msg	`{key}` must be a string	`{key}` має бути рядком
diff --git a/crates/ui-egui/src/i18n/vi.tsv b/crates/ui-egui/src/i18n/vi.tsv
index 149cb4702..899e9aff9 100644
--- a/crates/ui-egui/src/i18n/vi.tsv
+++ b/crates/ui-egui/src/i18n/vi.tsv
@@ -3800,6 +3800,7 @@ theme	Appearance	Giao diện
 @msg	`{id}` has no envelope dialog	`{id}` không có hộp thoại Envelope
 @msg	`{keep}` is not a side of this axis	`{keep}` không phải là một cạnh của trục này
 @msg	`{key}` must be `auto` or a language code such as `en` or `zh-hant`	`{key}` phải là `auto` hoặc mã ngôn ngữ như `en` hoặc `zh-hant`
+@msg	`{key}` must be a #rrggbb color	`{key}` phải là màu #rrggbb
 @msg	`{key}` must be a #rrggbb colour	`{key}` phải là màu #rrggbb
 @msg	`{key}` must be a number	`{key}` phải là một số
 @msg	`{key}` must be a string	`{key}` phải là một chuỗi
diff --git a/docs/mcp.md b/docs/mcp.md
index ea9386749..9fc88c525 100644
--- a/docs/mcp.md
+++ b/docs/mcp.md
@@ -815,13 +815,29 @@ is refused the same way:
 → invalid parameters for `effect.apply`: unknown parameter `blurr`; the command takes: radius
 ```
 
+The `color` of Drop Shadow, Inner Glow, Outer Glow and Shift to Color must be one the effect can read: a hex color
+(`#rrggbb`, `#rgb` or `#rrggbbaa`, with or without the `#`), `black`, `white`, `red`, `green` or `blue`, `[r, g, b]`
+(three numbers, each read on a 0 to 1 scale), or a color object (`{"model": "rgb", "r": 1, "g": 0, "b": 0}`).
+`effect.apply` and `effect.setParams` refuse any other value themselves (where the parameter check runs first, a number
+or a boolean is refused as not a string), so the app's effect dialogs and Appearance panel, a step of
+`command.batch` and a replayed journal get the same error, and the document and its undo history stay as they were:
+
+```json
+{"id": "effect.setParams", "params": {"index": 0, "params": {"color": "#ff00"}}}
+→ invalid parameters for `effect.setParams`: `color` must be a #rrggbb color
+```
+
+A document saved with such a color opens as before, and the effect draws its default color (an array of three or more
+entries reads an entry that isn't a number as 0).
+
 A number outside the range the effect documents is still stored as given and clamped when the effect draws. A
 plug-in effect's parameters are resolved against its manifest instead, and `effect.setParams` as a step of
-`command.batch` isn't checked (the effect it edits may only exist once the steps before it ran). A description with a `…` entry takes more keys than it lists: those of the command it names
+`command.batch` isn't checked before the batch runs (the effect it edits may only exist once the steps before it ran);
+the command still refuses an effect `color` it can't read. A description with a `…` entry takes more keys than it lists: those of the command it names
 (`…settings as file.new`), or any key when it names none, as `document.export` and `document.save` do for the options
 of the format they write (one object can carry several formats' options). A command that takes its own reply back
 (`document.setup`, `text.areaOptions`) says so the same way. The app's own journal isn't checked: an action or
-journal recorded by an older version replays as it did.
+journal recorded by an older version replays as it did, except for an effect `color` that the effect can't read.
 
 A step can use an earlier step's result, in `run` as in the `command_batch` tool. A parameter string that is exactly
 `$N` or `$N.path` takes that value from the result of step `N` (counting from 0, in the order they ran; `run --in`'s