English spelling for gray. RGBA is the same (0.5, 0.5, 0.5, 1).

	// Assign a grey color to this transform's material
	transform.renderer.material.color = Color.grey;

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void Example() {
        transform.renderer.material.color = Color.grey;
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def Example() as void:
		transform.renderer.material.color = Color.grey