Unity 2017 文字颜色渐变

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

[AddComponentMenu("UI/Effects/GradientText")]
public class GradientText : BaseMeshEffect
{
    [SerializeField]
    private Color32 topColor = Color.white;

    [SerializeField]
    private Color32 bottomColor = Color.black;

    public override void ModifyMesh(VertexHelper vh)
    {
        if (!IsActive() || vh.currentVertCount == 0)
            return;
        List<UIVertex> vertices =  new List<UIVertex>();
        vh.GetUIVertexStream(vertices);
        float bottomY = vertices[0].position.y;
        float topY = vertices[0].position.y;
        for (int i = 1; i < vertices.Count; i++ )
        {
           if( vertices[i].position.y > topY) {
                topY = vertices[i].position.y;
            }
            else if (vertices[i].position.y < bottomY)
            {
                bottomY = vertices[i].position.y;
            }
        }
        float uiElementHeight = topY- bottomY;
        UIVertex v = new UIVertex();
        for (int i = 0; i<vh.currentVertCount; i++)
        {
        vh.PopulateUIVertex(ref v, i);
        v.color = Color32.Lerp(bottomColor, topColor, (v.position.y - bottomY) / uiElementHeight);
        vh.SetUIVertex(v, i);
        }
    }
}