Default color types to opaque white

We choose an opaque color because otherwise the `OpaqueColor`
would have a substantially different default value than the
other color types.

White is the same as the default color within `bevy_color`.

The default color is used by the Brush in Parley and likely other places.

CHANGELOG.md

@@ -28,6 +28,7 @@ This release has an [MSRV][] of 1.82.
 * `AlphaColor`, `OpaqueColor`, and `PremulColor` now impl `PartialEq`. ([#76][] by [@waywardmonkeys][])
 * `HueDirection` now impls `PartialEq`. ([#79][] by [@waywardmonkeys][])
 * `ColorSpaceTag` and `HueDirection` now have bytemuck support. ([#81][] by [@waywardmonkeys][])
+* `AlphaColor`, `DynamicColor`, `OpaqueColor`, and `PremulColor` now default to an opaque white. ([#85][] by [@waywardmonkeys][])
 
 ### Changed
 
@@ -61,7 +62,8 @@ This is the initial release.
 [#78]: https://github.com/linebender/color/pull/78
 [#79]: https://github.com/linebender/color/pull/79
 [#80]: https://github.com/linebender/color/pull/80
-[#81]: https://github.com/linebender/color/pull/80
+[#81]: https://github.com/linebender/color/pull/81
+[#85]: https://github.com/linebender/color/pull/85
 
 [Unreleased]: https://github.com/linebender/color/compare/v0.1.0...HEAD
 [0.1.0]: https://github.com/linebender/color/releases/tag/v0.1.0

color/src/color.rs

@@ -21,6 +21,9 @@ use crate::floatfuncs::FloatFuncs;
 /// major motivation for including these is to enable weighted sums, including
 /// for spline interpolation. For cylindrical color spaces, hue fixup should
 /// be applied before interpolation.
+///
+/// The default value is an opaque white. We don't recommend relying upon this
+/// default.
 #[derive(Clone, Copy, Debug, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[repr(transparent)]
@@ -37,6 +40,9 @@ pub struct OpaqueColor<CS> {
 ///
 /// A color in a color space known at compile time, with an alpha channel.
 ///
+/// The default value is an opaque white. We don't recommend relying upon this
+/// default.
+///
 /// See [`OpaqueColor`] for a discussion of arithmetic traits and interpolation.
 #[derive(Clone, Copy, Debug, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
@@ -60,6 +66,9 @@ pub struct AlphaColor<CS> {
 /// the hue channel is not premultiplied. If it were, interpolation would
 /// give undesirable results.
 ///
+/// The default value is an opaque white. We don't recommend relying upon this
+/// default.
+///
 /// See [`OpaqueColor`] for a discussion of arithmetic traits and interpolation.
 #[derive(Clone, Copy, Debug, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
@@ -637,6 +646,26 @@ impl<CS: ColorSpace> PremulColor<CS> {
     }
 }
 
+// Defaults
+
+impl<CS: ColorSpace> Default for AlphaColor<CS> {
+    fn default() -> Self {
+        Self::WHITE
+    }
+}
+
+impl<CS: ColorSpace> Default for OpaqueColor<CS> {
+    fn default() -> Self {
+        Self::WHITE
+    }
+}
+
+impl<CS: ColorSpace> Default for PremulColor<CS> {
+    fn default() -> Self {
+        Self::WHITE
+    }
+}
+
 // Lossless conversion traits.
 
 impl<CS: ColorSpace> From<OpaqueColor<CS>> for AlphaColor<CS> {

color/src/dynamic.rs

@@ -6,6 +6,7 @@
 use crate::{
     color::{add_alpha, fixup_hues_for_interpolate, split_alpha},
     AlphaColor, ColorSpace, ColorSpaceLayout, ColorSpaceTag, HueDirection, LinearSrgb, Missing,
+    Srgb,
 };
 use core::hash::{Hash, Hasher};
 
@@ -25,6 +26,9 @@ use core::hash::{Hash, Hasher};
 /// When manipulating components directly, setting them nonzero when the
 /// corresponding missing flag is set may yield unexpected results.
 ///
+/// The default value is an opaque white in the [sRGB](Srgb) colorspace with
+/// no missing components. We don't recommend relying upon this default.
+///
 /// [Oklch]: crate::Oklch
 #[derive(Clone, Copy, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
@@ -365,6 +369,16 @@ impl DynamicColor {
     }
 }
 
+impl Default for DynamicColor {
+    fn default() -> Self {
+        Self {
+            cs: ColorSpaceTag::Srgb,
+            missing: Missing::default(),
+            components: add_alpha(Srgb::WHITE_COMPONENTS, 1.),
+        }
+    }
+}
+
 impl Hash for DynamicColor {
     /// The hash is computed from the bit representation of the component values.
     /// That makes it suitable for use as a cache key or memoization, but does not