var other : GameObject; 
other.renderer.material.color = Color.green;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public GameObject other;
    void Example() {
        other.renderer.material.color = Color.green;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public other as GameObject

    def Example():
        other.renderer.material.color = Color.green