Update changeset to reflect naming changes

Signed-off-by: James Turley <jamesturley@gocardless.com>

.changeset/grumpy-pugs-report.md

@@ -8,16 +8,16 @@ Add new way to override color selection to progress bar/gauge components.
 which is a function of the type:
 
 ```ts
-export type GetColor = (args: {
+export type GaugePropsGetColor = (args: {
   palette: Palette;
   value: number;
   inverse?: boolean;
   max?: number;
-}) => string | PaletteColor;
+}) => string;
 ```
 
-Either return a standard Material UI palette color object or a CSS color
-string (e.g. "red", "#f02020"), and the gauge will be set to that color.
+Return a standard CSS color string (e.g. "red", "#f02020"), and the gauge will
+be set to that color.
 
 If the prop is omitted, the default implementation is unchanged from previous
 versions.