Add Colour0 to OverlayColourProvider

osu.Game/Overlays/OverlayColourProvider.cs

@@ -29,6 +29,7 @@ namespace osu.Game.Overlays
         // The difference as to which should be used where comes down to context.
         // If the colour in question is supposed to always match the view in which it is displayed theme-wise, use `OverlayColourProvider`.
         // If the colour usage is special and in general differs from the surrounding view in choice of hue, use the `OsuColour` constants.
+        public Color4 Colour0 => getColour(1, 0.8f);
         public Color4 Colour1 => getColour(1, 0.7f);
         public Color4 Colour2 => getColour(0.8f, 0.6f);
         public Color4 Colour3 => getColour(0.6f, 0.5f);