ColorExtensionMethods.cs

using UnityEngine;

namespace Kogane
{
    public static class ColorExtensionMethods
    {
        public static Color Brighten
        (
            this Color color,
            float      amount
        )
        {
            Color.RGBToHSV( color, out var h, out var s, out var v );
            return Color.HSVToRGB( h, s, Mathf.Clamp01( v + amount ) );
        }

        public static Color Darken
        (
            this Color color,
            float      amount
        )
        {
            Color.RGBToHSV( color, out var h, out var s, out var v );
            return Color.HSVToRGB( h, s, Mathf.Clamp01( v - amount ) );
        }
    }
}