fix(editor): wrong style of mindmap in dark mode (#9462)

<div class='graphite__hidden'>
          <div>🎥 Video uploaded on Graphite:</div>
            <a href="https://app.graphite.dev/media/video/8ypiIKZXudF5a0tIgIzf/87aa060a-12c3-46dc-85fd-28980ba5b2bd.mov">
              <img src="https://app.graphite.dev/api/v1/graphite/video/thumbnail/8ypiIKZXudF5a0tIgIzf/87aa060a-12c3-46dc-85fd-28980ba5b2bd.mov">
            </a>
          </div>
<video src="https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/8ypiIKZXudF5a0tIgIzf/87aa060a-12c3-46dc-85fd-28980ba5b2bd.mov">Screen Recording 2024-12-31 at 18.05.36.mov</video>

blocksuite/affine/model/src/elements/shape/shape.ts

@@ -148,7 +148,7 @@ export class ShapeElementModel extends GfxPrimitiveElementModel<ShapeProps> {
     blur: number;
     offsetX: number;
     offsetY: number;
-    color: string;
+    color: Color;
   } | null = null;
 
   @field()
@@ -234,7 +234,7 @@ export class LocalShapeElementModel extends GfxLocalElementModel {
     blur: number;
     offsetX: number;
     offsetY: number;
-    color: string;
+    color: Color;
   } | null = null;
 
   @prop()