public static Color WithSaturation(this Color col, float saturation)
        {
            float4 v   = col.ToFloat4();
            float3 hsv = RGBtoHSV(v.xyz);

            hsv.y = saturation;
            v.xyz = HSVtoRGB(hsv);
            return(v.ToColor());
        }
        public static Color WithLightness(this Color col, float lightness)
        {
            float4 f4  = col.ToFloat4();
            float3 hsl = RGBtoHSL(f4.xyz);

            hsl.z  = lightness;
            f4.xyz = HSLtoRGB(hsl);
            return(f4.ToColor());
        }