Be explicit about CPAL color space

The OpenType specification defines that this data is sRGB and
Skrifa follows along. Be clear about it here though as even
if other things change with color, this should be sure to be
interpreting that data correctly.

vello/src/scene.rs

@@ -6,7 +6,7 @@ mod bitmap;
 use std::sync::Arc;
 
 use peniko::{
-    color::{palette, DynamicColor, Srgb},
+    color::{palette, AlphaColor, DynamicColor, Srgb},
     kurbo::{Affine, BezPath, Point, Rect, Shape, Stroke, Vec2},
     BlendMode, Blob, Brush, BrushRef, Color, ColorStop, ColorStops, ColorStopsSource, Compose,
     Extend, Fill, Font, Gradient, Image, Mix, StyleRef,
@@ -979,7 +979,9 @@ fn conv_brush(
     }
 }
 
-fn color_index(cpal: &'_ Cpal<'_>, palette_index: u16) -> Option<Color> {
+// The OpenType color palette is defined to be using the sRGB color space.
+// <https://learn.microsoft.com/en-us/typography/opentype/spec/cpal#palette-entries-and-color-records>
+fn color_index(cpal: &'_ Cpal<'_>, palette_index: u16) -> Option<AlphaColor<Srgb>> {
     // The "application determined" foreground color should be used
     // This will be handled by the caller
     if palette_index == 0xFFFF {
@@ -988,7 +990,7 @@ fn color_index(cpal: &'_ Cpal<'_>, palette_index: u16) -> Option<Color> {
     let actual_colors = cpal.color_records_array().unwrap().unwrap();
     // TODO: Error reporting in the `None` case
     let color = actual_colors.get(usize::from(palette_index))?;
-    Some(Color::from_rgba8(
+    Some(AlphaColor::<Srgb>::from_rgba8(
         color.red,
         color.green,
         color.blue,