Effects: effect.apply and effect.setParams refuse a color the effect can't draw

effect.apply and effect.setParams stored any string as the color of
Drop Shadow, Inner Glow, Outer Glow and Shift to Color. When the
effect could not read it, it drew its default color with no message,
so a typo such as #ff00 in the Drop Shadow dialog turned the shadow
black.

The commands now refuse such a color before they edit, with
"`color` must be a #rrggbb color", and the document and its undo
history stay as they were. Hex colors, the five named colors,
[r, g, b] and color objects still pass. The check runs in the
commands, so the app, command.batch steps and replayed journals get
it too. The effect dialog's OK shows the error and keeps the dialog
open, with Preview on or off. Saved documents open as before.

Docs: docs/mcp.md (effect params).

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)? {