如何通过脚本为材质的alpha属性设置动画？

Question

我正在基于分配给动画器组件的当前控制器通过脚本创建Animator OverrideController。我已经为位置创建了动画曲线，并且该曲线有效。当我尝试为透明度（材质颜色alpha）设置动画时，它不起作用。我是否无法正确访问此属性？

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class AnimationScript : MonoBehaviour {

    void Start()
    {
        AnimationClip clip = new AnimationClip();

        AnimationCurve curve = AnimationCurve.EaseInOut(0.0f, transform.position.x, 1.0f, transform.position.x);
        clip.SetCurve("", typeof(Transform), "localPosition.x", curve);

        curve = AnimationCurve.Linear(0.0f, 1.0f, 1.0f, 0.0f);
        clip.SetCurve("", typeof(Material), "_Color.a", curve);

        Animator anim = GetComponent<Animator>();
        AnimatorOverrideController animatorOverrideController = new AnimatorOverrideController(anim.runtimeAnimatorController);
        // "loop" is the name of clip not name of state
        animatorOverrideController["loop"] = clip;
        anim.runtimeAnimatorController = animatorOverrideController;
    }

}

但是，旧版动画组件的类似代码有效：

void Start()
{
    Animation anim = GetComponent<Animation>();
    AnimationCurve curve;

    // create a new AnimationClip
    AnimationClip clip = new AnimationClip();
    clip.legacy = true;

    // update the clip to a change color
    curve = AnimationCurve.Linear(0.0f, 1.0f, 2.0f, 0.0f);
    clip.SetCurve("", typeof(Material), "_Color.a", curve);

    // now animate the GameObject
    anim.AddClip(clip, clip.name);
    anim.Play(clip.name);
}

我缺少什么，为什么第一个脚本不起作用？