diff --git a/crates/doc/src/props.rs b/crates/doc/src/props.rs
index 97d653572..768625d4c 100644
--- a/crates/doc/src/props.rs
+++ b/crates/doc/src/props.rs
@@ -31,13 +31,42 @@ impl Rgb {
 }
 
 /// A text colour: automatic (black on light backgrounds, white on dark) or a fixed colour.
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize, Default)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Default)]
 pub enum TextColor {
     #[default]
     Auto,
     Rgb(Rgb),
 }
 
+impl TextColor {
+    /// `auto` or `automatic` (any case), or a colour [`Rgb::parse`] reads.
+    pub fn parse(s: &str) -> Option<TextColor> {
+        if s.eq_ignore_ascii_case("auto") || s.eq_ignore_ascii_case("automatic") { Some(TextColor::Auto) } else { Rgb::parse(s).map(TextColor::Rgb) }
+    }
+}
+
+impl<'de> Deserialize<'de> for TextColor {
+    /// Reads what it writes (`"Auto"`, `{"Rgb": [r, g, b]}`) and also a string [`TextColor::parse`]
+    /// reads, so `styles.modify` and `format.set` take the colours `format.color` takes.
+    fn deserialize<D: serde::Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
+        use serde::de::{Error, Unexpected};
+        #[derive(Deserialize)]
+        enum Written {
+            Auto,
+            Rgb(Rgb),
+        }
+        match serde_json::Value::deserialize(d)? {
+            serde_json::Value::String(s) => {
+                TextColor::parse(&s).ok_or_else(|| D::Error::invalid_value(Unexpected::Str(&s), &"`auto`, `RRGGBB` or `#RRGGBB`"))
+            }
+            v => Ok(match serde_json::from_value(v).map_err(D::Error::custom)? {
+                Written::Auto => TextColor::Auto,
+                Written::Rgb(c) => TextColor::Rgb(c),
+            }),
+        }
+    }
+}
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize, Default)]
 #[serde(rename_all = "camelCase")]
 pub enum Underline {
@@ -1125,6 +1154,27 @@ mod tests {
         assert_eq!(TextDirection::from_ooxml("é?"), TextDirection::Horizontal);
     }
 
+    /// #865: a colour reads as `format.color` takes it (`RRGGBB`, `#RRGGBB`, `auto`), while what
+    /// documents and settings already hold reads and writes exactly as before.
+    #[test]
+    fn text_color_reads_hex_and_keeps_its_serialized_forms() {
+        let read = |j: &str| serde_json::from_str::<TextColor>(j);
+        let ink = TextColor::Rgb(Rgb(0x1B, 0x16, 0x11));
+        assert_eq!(read(r#""1B1611""#).unwrap(), ink);
+        assert_eq!(read(r##""#1b1611""##).unwrap(), ink);
+        assert_eq!(read(r#""auto""#).unwrap(), TextColor::Auto);
+        assert_eq!(read(r#""Automatic""#).unwrap(), TextColor::Auto);
+        for (c, j) in [(TextColor::Auto, r#""Auto""#), (ink, r#"{"Rgb":[27,22,17]}"#)] {
+            assert_eq!(serde_json::to_string(&c).unwrap(), j, "written as before");
+            assert_eq!(read(j).unwrap(), c);
+        }
+        for bad in [r#""1B161""#, r#""zzzzzz""#, r#""""#, r#"{"Rgb":"1B1611"}"#, r#"{"Hex":[1,2,3]}"#, "7", "[27,22,17]"] {
+            assert!(read(bad).is_err(), "{bad}");
+        }
+        let p: CharProps = serde_json::from_value(serde_json::json!({"color": "#1B1611", "bold": true})).unwrap();
+        assert_eq!((p.color, p.bold), (Some(ink), Some(true)));
+    }
+
     #[test]
     fn props_serde_skip_none() {
         let p = CharProps { bold: Some(true), ..Default::default() };
diff --git a/crates/engine/src/cmd/format.rs b/crates/engine/src/cmd/format.rs
index 85ca49e13..dc5503d22 100644
--- a/crates/engine/src/cmd/format.rs
+++ b/crates/engine/src/cmd/format.rs
@@ -361,11 +361,7 @@ fn nudge_size(s: &mut Session, d: f32) -> CmdResult {
 
 fn color(s: &mut Session, v: &Value) -> CmdResult {
     let c = p::req_str(v, "color")?;
-    let tc = if c.eq_ignore_ascii_case("auto") || c.eq_ignore_ascii_case("automatic") {
-        TextColor::Auto
-    } else {
-        TextColor::Rgb(Rgb::parse(c).ok_or_else(|| CmdError::Params("color must be RRGGBB or auto".into()))?)
-    };
+    let tc = TextColor::parse(c).ok_or_else(|| CmdError::Params("color must be RRGGBB or auto".into()))?;
     apply(s, &|x| x.color = Some(tc))
 }
 
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 785c11d25..624b3aa76 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -2471,6 +2471,35 @@ fn styles_apply_multi_paragraph_selection() {
     }
 }
 
+/// #865: `styles.modify` takes a colour the way `format.color` does (`RRGGBB`, `#RRGGBB`, `auto`),
+/// still reads the serialized forms, and rejects a bad colour without touching the style.
+#[test]
+fn modify_style_takes_hex_colours_like_format_color() {
+    use wordcraft_doc::{CharProps, Rgb, TextColor};
+    let mut s = s();
+    let color = |s: &Session| s.doc.styles.get("Heading1").and_then(|st| st.chr.color);
+    let modify = |s: &mut Session, c: serde_json::Value| s.run("styles.modify", &json!({"style": "Heading1", "chr": {"color": c}}));
+
+    modify(&mut s, json!("1B1611")).unwrap();
+    assert_eq!(color(&s), Some(TextColor::Rgb(Rgb(0x1B, 0x16, 0x11))));
+    modify(&mut s, json!("auto")).unwrap();
+    assert_eq!(color(&s), Some(TextColor::Auto));
+    modify(&mut s, json!("#1B1611")).unwrap();
+    assert_eq!(color(&s), Some(TextColor::Rgb(Rgb(0x1B, 0x16, 0x11))));
+    modify(&mut s, json!("Auto")).unwrap();
+    assert_eq!(color(&s), Some(TextColor::Auto));
+    modify(&mut s, json!({"Rgb": [192, 0, 0]})).unwrap();
+    let red = TextColor::Rgb(Rgb(0xC0, 0, 0));
+    assert_eq!(color(&s), Some(red));
+    assert_eq!(s.doc.styles.resolve_char(Some("Heading1"), &CharProps::default()).color, red);
+
+    for bad in [json!("1B16"), json!("not a colour"), json!({"Rgb": "1B1611"}), json!(7)] {
+        let r = modify(&mut s, bad.clone());
+        assert!(matches!(r, Err(crate::CmdError::Params(_))), "{bad}: {r:?}");
+        assert_eq!(color(&s), Some(red), "{bad} leaves the style alone");
+    }
+}
+
 /// #555: Update Heading 2 to Match Selection (the styles pane's context menu) makes Heading 2
 /// look like the selected text — its paragraph style and direct formatting — so every Heading 2
 /// paragraph changes; the selected paragraph takes Heading 2, and it is one undo step.