参考文档：https://docs.unity3d.com/ScriptReference/Shader.Find.html
改变color的alpha即可。
关键：Transparent/Diffuse
Material material = new Material(Shader.Find("Transparent/Diffuse"));
material.color = Color.green;
GetComponent<Renderer>().material = material;
原文：http://www.cnblogs.com/makebetter/p/6747012.html