allow changing the color of overview decorations

src/common/services/DecorationService.ts

@@ -60,6 +60,8 @@ class Decoration extends Disposable implements IInternalDecoration {
   private _onDispose = this.register(new EventEmitter<void>());
   public readonly onDispose = this._onDispose.event;
 
+  public overviewRulerDecorationColor: string | undefined;
+
   constructor(
     public readonly options: IDecorationOptions
   ) {