自定义颜色透明度如何实现？

@Entry  
@Component  
struct Index {  
  @State message: string = 'Hello World';  
  @State opacityValue: number = 1;  
  
  getColor() {  
    return `rgba(222,33,44,${this.opacityValue})`  
  }  
  
  build() {  
    Row() {  
      Column({ space: 10 }) {  
        Text(this.message)  
          .fontSize(50)  
          .fontWeight(FontWeight.Bold)  
          .fontColor(this.getColor())  
  
        Button('0').onClick(() => {  
          this.opacityValue = 0;  
        })  
        Button('0.5').onClick(() => {  
          this.opacityValue = 0.5;  
        })  
        Button('1').onClick(() => {  
          this.opacityValue = 1;  
        })  
  
      }  
      .width('100%')  
    }  
    .height('100%')  
  }  
}

private getColor(colorName: string, opacity: number = 1) {  
  let opacityStr = Math.max(0, Math.min(Math.round(opacity * 255), 255)).toString(16).padStart(2, '0').toLowerCase();  
  
  const colorValue = getContext(this).resourceManager.getColorByNameSync(colorName).toString(16);  
  
  return '#' + opacityStr + colorValue.substring(2);  
}