Unity - Scripting API:

public static operator /(a: Color, b: float): Color;

public static Color operator /(Color a, float b);

Parameters

Divides color a by the float b. Each color component is scaled separately.

// white / 2 = gray
var grayColor : Color = Color.white / 2;

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public Color grayColor = Color.white / 2;
}