HarmonyOS 鸿蒙Next Canvas绘制的颜色无法使用颜色资源

参考以下demo：

//EntryAbility.ets

 onForeground(): void {
   // Ability has brought to foreground
   hilog.info(0x0000, 'testTag', '%{public}s', 'Ability onForeground');
   console.info('app is foreground');
   let context = GlobalContext.getContext().getObject('Context') as common.Context
   let a = context?.resourceManager.getColorSync($r('app.color.start_window_background'))
   console.info('onForeground: '+a?.toString())
 }


// Index.ets
import { GlobalContext } from './GlobalContext';
import { common } from '[@kit](/user/kit).AbilityKit';
[@Entry](/user/Entry)
[@Component](/user/Component)
struct Index {
 private settings: RenderingContextSettings = new RenderingContextSettings(true)
 private context: CanvasRenderingContext2D = new CanvasRenderingContext2D(this.settings)
 private offCanvas: OffscreenCanvas = new OffscreenCanvas(600, 600)
 aboutToAppear(): void {
   let context = getContext(this)
   GlobalContext.getContext().setObject('Context', context)
   let context1 = GlobalContext.getContext().getObject('Context') as common.Context
   let a = context1?.resourceManager.getColorSync($r('app.color.start_window_background'))
   console.info('aboutToAppear: '+a?.toString())
 }
 build() {
   Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Center, justifyContent: FlexAlign.Center }) {
     Canvas(this.context)
       .width('100%')
       .height('100%')
       .backgroundColor('#ffff00')
       .onReady(() => {
         let a = getContext(this).resourceManager.getColorSync($r('app.color.start_window_background'))
         let offContext = this.offCanvas.getContext("2d", this.settings)
         offContext.shadowBlur = 30
         offContext.shadowColor = a.toString()
         offContext.fillStyle = a.toString()
         offContext.fillRect(30, 30, 100, 100)
         let image = this.offCanvas.transferToImageBitmap()
         this.context.transferFromImageBitmap(image)
       })
   }
   .width('100%')
   .height('100%')
 }
}


//GlobalContext.ets
export class GlobalContext {
 private constructor() {
 }
 private static instance: GlobalContext;
 private _objects = new Map<string, Object>();
 public static getContext(): GlobalContext {
   if (!GlobalContext.instance) {
     GlobalContext.instance = new GlobalContext();
   }
   return GlobalContext.instance;
 }
 getObject(value: string): Object | undefined {
   return this._objects.get(value);
 }
 setObject(key: string, objectClass: Object): void {
   this._objects.set(key, objectClass);
 }
}