unity更改文字透明度

话不多说，直接上代码。

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
public class testtest : MonoBehaviour {
    Color changeColor;
    public Text TextTest;
    // Use this for initialization
    void Start ()
    {
        changeColor = TextTest.color;

    }

    // Update is called once per frame
    void Update () {
		if(Input.GetKeyDown(KeyCode.A))
        {
            //白色半透明
            changeColor.r = 1f;
            changeColor.g =1f;
            changeColor.b = 1f;
            changeColor.a = 0.5f;
            TextTest.color = changeColor;
        }
        if (Input.GetKeyDown(KeyCode.D))
        {
　　　　　　//白色不透明
            changeColor.a = 1f;
            changeColor.r = 1f;
            changeColor.g = 1f;
            changeColor.b = 1f;
            TextTest.color = changeColor;
        }
	}
}