HarmonyOS overlay是控制图片的填充方式，如何设置颜色遮罩？

@Entry  
@Component  
struct List_Mask {  
  private arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]  
  build() {  
    Column() {  
      List({ space: 20, initialIndex: 0 }) {  
        ForEach(this.arr, (item: number) => {  
          ListItem() {  
            MyListItem_Mask({ item })  
          }  
        }, (item: string) => item)  
      }  
      .listDirection(Axis.Vertical) // 排列方向  
      .scrollBar(BarState.Off)  
      .friction(0.6)  
      .divider({  
        strokeWidth: 2,  
        color: 0xFFFFFF,  
        startMargin: 20,  
        endMargin: 20  
      }) // 每行之间的分界线  
      .edgeEffect(EdgeEffect.Spring) // 边缘效果设置为Spring  
      .width('90%')  
    }  
    .width('100%')  
    .height('100%')  
    .backgroundColor(0xDCDCDC)  
    .padding({ top: 5 })  
  }  
}  
@Component  
struct MyListItem_Mask {  
  @State isMask: boolean = false  
  @Prop item: number  
  @Builder  overBuilder() {  
    Row() {  
    }  
    .backgroundColor("#50000000")  
  }  
  build() {  
    Stack() {  
      Image($r('app.media.mid'))  
        .draggable(false)  
        .overlay(this.overBuilder())   
        .objectFit(ImageFit.Contain)  
    }  
    .height(100)  
    .width('100%')  
    .borderRadius(10)  
    .backgroundColor(0xFFFFFF)  
  }  
}