Unity3d 如何更改Button的背景色

using UnityEngine;
using System.Collections; 
public class ButtonStyle : MonoBehaviour {
	public Color _color;//在编辑环境下选择背景色，透明度不能为0
	public Texture2D tex;
 
 void OnGUI(){GUI.Button(new Rect(0,0,100,100),"tex");Color oldColor = GUI.backgroundColor;//保存原有的背景色GUI.backgroundColor = _color;//更改背景色GUI.Button (new Rect (650,20,150,120), tex);//这个按钮的背景色发生了变化 GUI.backgroundColor = oldColor;//恢复原来的背景色GUI.Button(new
 Rect(140,100,100,100),"tex");//这个按钮恢复了以前的背景色}}

public Button button;
void Start()
{
ColorBlock cb = new ColorBlock();
cb.nORMalColor = Color.red;
cb.highlightedColor = Color.green;
cb.pressedColor = Color.blue;
cb.disabledColor = Color.black;
button.colors = cb
}