Scripting Reference
Component.guiTexture

var guiTexture : GUITexture

Description

The GUITexture attached to this GameObject (Read Only). (null if there is none attached)

JavaScript 
guiTexture.color = Color.blue;
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        guiTexture.color = Color.blue;
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        guiTexture.color = Color.blue