GUIStyle.active 激活

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
	public Texture2D aTexture;
	void OnGUI() {
		if (!typeof(aTexture)) {
			Debug.LogError("Assign a texture on the editor first");
			return;
		}
		if (GUI.skin.customStyles.Length > 0)
			GUI.skin.customStyles[0].active.background = aTexture;

	}
}

// Assigns a texture to customStyles[0] for when the control
// is pressed down
//当控件被按下时，指定一个纹理到customStyles[0]

var aTexture : Texture2D;

function OnGUI() {
    if(!aTexture) {
		Debug.LogError("Assign a texture on the editor first");
    	return;
    }
    if(GUI.skin.customStyles.Length > 0)
		GUI.skin.customStyles[0].active.background = aTexture;
}