// change the color of the texture to green
guiTexture.color = Color.green;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void Awake() {
guiTexture.color = Color.green;
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def Awake():
guiTexture.color = Color.green