Color.operator -

public static operator -(a: Color, b: Color): Color;

public static Color operator -(Color a, Color b);

Parameters

Subtracts color b from color a. Each component is subtracted separately.

// magenta - blue = red
var redColor : Color = Color.magenta - Color.blue;

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public Color redColor = Color.magenta - Color.blue;
}