Color.operator Color  

// Convert a vector4 to a Color
var aColor : Color = Vector4(0.5,1,0.5,1);

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Color aColor = new Vector4(0.5F, 1, 0.5F, 1);
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public aColor as Color = Vector4(0.5F, 1, 0.5F, 1)