diff --git a/crates/color/src/lib.rs b/crates/color/src/lib.rs
index 9af14253d..5de064d6b 100644
--- a/crates/color/src/lib.rs
+++ b/crates/color/src/lib.rs
@@ -111,6 +111,16 @@ impl Color {
     pub fn out_of_gamut(&self) -> bool {
         cms::active().out_of_gamut(self)
     }
+    /// The colour exactly, as a key: its model and its components' bits (colours that only look
+    /// alike, as a grey and the same RGB grey, differ).
+    pub fn key(&self) -> [u32; 5] {
+        match *self {
+            Color::Rgb { r, g, b } => [0, r.to_bits(), g.to_bits(), b.to_bits(), 0],
+            Color::Cmyk { c, m, y, k } => [1, c.to_bits(), m.to_bits(), y.to_bits(), k.to_bits()],
+            Color::Gray { k } => [2, k.to_bits(), 0, 0, 0],
+            Color::Lab { l, a, b } => [3, l.to_bits(), a.to_bits(), b.to_bits(), 0],
+        }
+    }
     pub fn to_rgba8(&self, alpha: f32) -> [u8; 4] {
         let [r, g, b] = self.to_rgb();
         let q = |v: f32| (v.clamp(0.0, 1.0) * 255.0).round() as u8;
diff --git a/crates/text/src/fontdb.rs b/crates/text/src/fontdb.rs
index a459e0491..a1b232bc4 100644
--- a/crates/text/src/fontdb.rs
+++ b/crates/text/src/fontdb.rs
@@ -425,8 +425,8 @@ type GlyphImages = GlyphCache<(u32, u32), Arc<GlyphImage>>;
 /// [`FontDb::glyph_colour`]'s answers by face and glyph, and the text's fill and stroke colours for
 /// glyphs that paint with them.
 type GlyphColours = GlyphCache<(u32, u32, Option<TextColours>), ColourContent>;
-/// The text's fill and stroke colours, as a cache key.
-type TextColours = ([u8; 4], Option<[u8; 4]>);
+/// The text's fill and stroke colours, as a cache key ([`Color::key`]).
+type TextColours = ([u32; 5], Option<[u32; 5]>);
 
 /// What a glyph's colour content (an image, layers) takes of memory, in bytes.
 trait Weight {
@@ -2573,7 +2573,7 @@ impl FontDb {
         let svg = svg_drawn(face, &f, gid);
         // Kept without colours, or by the text's colours it uses: the fill, and for SVG art the
         // stroke too.
-        let coloured = Some((foreground.to_rgba8(1.0), stroke.filter(|_| svg).map(|c| c.to_rgba8(1.0))));
+        let coloured = Some((foreground.key(), stroke.filter(|_| svg).map(|c| c.key())));
         {
             let cache = self.colours.lock().unwrap_or_else(|e| e.into_inner());
             if let Some(c) = [None, coloured].iter().find_map(|k| cache.kept.get(&(face.id, gid, *k))) {
diff --git a/crates/text/src/tests_colr.rs b/crates/text/src/tests_colr.rs
index 6f1ad40a6..116eeff3c 100644
--- a/crates/text/src/tests_colr.rs
+++ b/crates/text/src/tests_colr.rs
@@ -189,6 +189,24 @@ fn the_foreground_layer_takes_the_runs_fill_and_black_for_a_gradient_fill() {
     assert_eq!(foreground(gradient), Paint::solid(Color::BLACK));
 }
 
+/// Fills that look alike but separate differently (a grey on the black plate, the same RGB grey on
+/// all four) each paint the foreground layer in their own colour.
+#[test]
+fn fills_that_only_look_alike_each_paint_the_foreground_layer() {
+    let db = colr_db(false);
+    let foreground = |fill: Color| {
+        let st = CharStyle { fill: Paint::solid(fill), ..colr_style(false) };
+        let l = layout(&db, &TextObject::point(KPoint::ZERO, &COLOUR_CHAR.to_string(), st));
+        let colour = l.glyphs[0].colour.clone().unwrap();
+        children(&colour)[1].appearance.fill_paint()
+    };
+    let grey = Color::gray(0.5);
+    let rgb = Color::rgb8(128, 128, 128);
+    assert_eq!(grey.to_rgba8(1.0), rgb.to_rgba8(1.0), "they look alike");
+    assert_eq!(foreground(grey), Paint::solid(grey));
+    assert_eq!(foreground(rgb), Paint::solid(rgb));
+}
+
 #[test]
 fn layout_bounds_take_in_the_colour_layers() {
     let db = colr_db(true);