DynamicColorGenExtensions.cs

public static class DynamicColorGenExtensions
    {
        //Find foreground color for a dynamic background color
        public static  Color FindForgroundColor(this Color color)
        {
            if (color.R <= 5 && color.G <= 5 && color.B <= 5)
            {
                return Color.WhiteSmoke;
            }

            var delta = 0.05d;
            var resultRatio = 4.5d;
            var colorHsl = (HSLColor)color;
            var lumocity = colorHsl.Luminosity;
            var resLumocity = 0d;
            double lightness;
            if (IsLightColor(color, out lightness))
            {
                //Find more darker color 
                resLumocity = ((lumocity + delta) / resultRatio) - delta;
            }
            else
            {
                //Find more lighter color 
                if (lightness <= 15)
                {
                    resultRatio = 21d - lightness;
                    delta = 0;
                }

                resLumocity = ((lumocity + delta) * resultRatio) - delta;
            }

            colorHsl.Luminosity = resLumocity;
            return (Color)colorHsl;
        }



        public static bool IsLightColor(Color bg, out double lightness)
        {
            //https://en.wikipedia.org/wiki/HSL_and_HSV#Lightness
            int nThreshold = 150;
            //int nThreshold = 128;
            lightness = ((bg.R * 0.299d) + (bg.G * 0.587d) +
                                          (bg.B * 0.114d));


            var bgDelta = (int)lightness;
            var isLight = (255 - bgDelta < nThreshold) ? true : false;

            //Console.WriteLine(string.Format(@"Color is {0} with delta {1} lightness {2}", isLight ? "Light" : "dark", bgDelta, lightness));
            return isLight;
        }


        //https://richnewman.wordpress.com/about/code-listings-and-diagrams/hslcolor-class/
        private class HSLColor
        {
            // Private data members below are on scale 0-1
            // They are scaled for use externally based on scale
            private double hue = 1.0;
            private double saturation = 1.0;
            private double luminosity = 1.0;

            private const double scale = 240.0;

            public double Hue
            {
                get { return hue * scale; }
                set { hue = CheckRange(value / scale); }
            }
            public double Saturation
            {
                get { return saturation * scale; }
                set { saturation = CheckRange(value / scale); }
            }
            public double Luminosity
            {
                get { return luminosity * scale; }
                set { luminosity = CheckRange(value / scale); }
            }

            private double CheckRange(double value)
            {
                if (value < 0.0)
                    value = 0.0;
                else if (value > 1.0)
                    value = 1.0;
                return value;
            }

            public override string ToString()
            {
                return String.Format("H: {0:#0.##} S: {1:#0.##} L: {2:#0.##}", Hue, Saturation, Luminosity);
            }

            public string ToRGBString()
            {
                Color color = (Color)this;
                return String.Format("R: {0:#0.##} G: {1:#0.##} B: {2:#0.##}", color.R, color.G, color.B);
            }

            #region Casts to/from System.Drawing.Color
            public static implicit operator Color(HSLColor hslColor)
            {
                double r = 0, g = 0, b = 0;
                if (hslColor.luminosity != 0)
                {
                    if (hslColor.saturation == 0)
                        r = g = b = hslColor.luminosity;
                    else
                    {
                        double temp2 = GetTemp2(hslColor);
                        double temp1 = 2.0 * hslColor.luminosity - temp2;

                        r = GetColorComponent(temp1, temp2, hslColor.hue + 1.0 / 3.0);
                        g = GetColorComponent(temp1, temp2, hslColor.hue);
                        b = GetColorComponent(temp1, temp2, hslColor.hue - 1.0 / 3.0);
                    }
                }
                return Color.FromArgb((int)(255 * r), (int)(255 * g), (int)(255 * b));
            }

            private static double GetColorComponent(double temp1, double temp2, double temp3)
            {
                temp3 = MoveIntoRange(temp3);
                if (temp3 < 1.0 / 6.0)
                    return temp1 + (temp2 - temp1) * 6.0 * temp3;
                else if (temp3 < 0.5)
                    return temp2;
                else if (temp3 < 2.0 / 3.0)
                    return temp1 + ((temp2 - temp1) * ((2.0 / 3.0) - temp3) * 6.0);
                else
                    return temp1;
            }
            private static double MoveIntoRange(double temp3)
            {
                if (temp3 < 0.0)
                    temp3 += 1.0;
                else if (temp3 > 1.0)
                    temp3 -= 1.0;
                return temp3;
            }
            private static double GetTemp2(HSLColor hslColor)
            {
                double temp2;
                if (hslColor.luminosity < 0.5)  //<=??
                    temp2 = hslColor.luminosity * (1.0 + hslColor.saturation);
                else
                    temp2 = hslColor.luminosity + hslColor.saturation - (hslColor.luminosity * hslColor.saturation);
                return temp2;
            }

            public static implicit operator HSLColor(Color color)
            {
                HSLColor hslColor = new HSLColor();
                hslColor.hue = color.GetHue() / 360.0; // we store hue as 0-1 as opposed to 0-360 
                hslColor.luminosity = color.GetBrightness();
                hslColor.saturation = color.GetSaturation();
                return hslColor;
            }
            #endregion

            public void SetRGB(int red, int green, int blue)
            {
                HSLColor hslColor = (HSLColor)Color.FromArgb(red, green, blue);
                this.hue = hslColor.hue;
                this.saturation = hslColor.saturation;
                this.luminosity = hslColor.luminosity;
            }

            public HSLColor() { }
            public HSLColor(Color color)
            {
                SetRGB(color.R, color.G, color.B);
            }
            public HSLColor(int red, int green, int blue)
            {
                SetRGB(red, green, blue);
            }
            public HSLColor(double hue, double saturation, double luminosity)
            {
                this.Hue = hue;
                this.Saturation = saturation;
                this.Luminosity = luminosity;
            }

        }

    }