HSL color, HSB color and RGB color types, as well as conversion methods between them in C# and .NET

ColorConverting.cs

namespace ZetaColorEditor.Colors;

using System;
using System.Drawing;

/// <summary>
/// Provides color conversion functionality.
/// </summary>
/// <remarks>
/// http://en.wikipedia.org/wiki/HSV_color_space
/// http://www.easyrgb.com/math.php?MATH=M19#text19
/// </remarks>
internal static class ColorConverting
{
    public static RgbColor ColorToRgb(
        Color color)
    {
        return new(color.R, color.G, color.B, color.A);
    }

    public static Color RgbToColor(
        RgbColor rgb)
    {
        return Color.FromArgb(rgb.Alpha, rgb.Red, rgb.Green, rgb.Blue);
    }

    public static HsbColor RgbToHsb(
        RgbColor rgb)
    {
        // _NOTE #1: Even though we're dealing with a very small range of
        // numbers, the accuracy of all calculations is fairly important.
        // For this reason, I've opted to use double data types instead
        // of float, which gives us a little bit extra precision (recall
        // that precision is the number of significant digits with which
        // the result is expressed).

        var r = rgb.Red / 255d;
        var g = rgb.Green / 255d;
        var b = rgb.Blue / 255d;

        var minValue = getMinimumValue(r, g, b);
        var maxValue = getMaximumValue(r, g, b);
        var delta = maxValue - minValue;

        double hue = 0;
        double saturation;
        var brightness = maxValue * 100;

        if (Math.Abs(maxValue - 0) < 0.00001 || Math.Abs(delta - 0) < 0.00001)
        {
            hue = 0;
            saturation = 0;
        }
        else
        {
			// _NOTE #2: FXCop insists that we avoid testing for floating 
			// point equality (CA1902). Instead, we'll perform a series of
			// tests with the help of 0.00001 that will provide 
			// a more accurate equality evaluation.

			if (Math.Abs(minValue - 0) < 0.00001)
            {
                saturation = 100;
            }
            else
            {
                saturation = delta / maxValue * 100;
            }

            if (Math.Abs(r - maxValue) < 0.00001)
            {
                hue = (g - b) / delta;
            }
            else if (Math.Abs(g - maxValue) < 0.00001)
            {
                hue = 2 + (b - r) / delta;
            }
            else if (Math.Abs(b - maxValue) < 0.00001)
            {
                hue = 4 + (r - g) / delta;
            }
        }

        hue *= 60;
        if (hue < 0)
        {
            hue += 360;
        }

        return new(
            hue,
            saturation,
            brightness,
            rgb.Alpha);
    }

    public static HslColor RgbToHsl(
        RgbColor rgb)
    {
        var varR = rgb.Red / 255.0; //Where RGB values = 0 ÷ 255
        var varG = rgb.Green / 255.0;
        var varB = rgb.Blue / 255.0;

        var varMin = getMinimumValue(varR, varG, varB); //Min. value of RGB
        var varMax = getMaximumValue(varR, varG, varB); //Max. value of RGB
        var delMax = varMax - varMin; //Delta RGB value

        double h;
        double s;
        var l = (varMax + varMin) / 2;

        if (Math.Abs(delMax - 0) < 0.00001) //This is a gray, no chroma...
        {
            h = 0; //HSL results = 0 ÷ 1
            s = 0;
            // UK:
            //				s = 1.0;
        }
        else //Chromatic data...
        {
            if (l < 0.5)
            {
                s = delMax / (varMax + varMin);
            }
            else
            {
                s = delMax / (2.0 - varMax - varMin);
            }

            var delR = ((varMax - varR) / 6.0 + delMax / 2.0) / delMax;
            var delG = ((varMax - varG) / 6.0 + delMax / 2.0) / delMax;
            var delB = ((varMax - varB) / 6.0 + delMax / 2.0) / delMax;

            if (Math.Abs(varR - varMax) < 0.00001)
            {
                h = delB - delG;
            }
            else if (Math.Abs(varG - varMax) < 0.00001)
            {
                h = 1.0 / 3.0 + delR - delB;
            }
            else if (Math.Abs(varB - varMax) < 0.00001)
            {
                h = 2.0 / 3.0 + delG - delR;
            }
            else
            {
                // Uwe Keim.
                h = 0.0;
            }

            if (h < 0.0)
            {
                h += 1.0;
            }
            if (h > 1.0)
            {
                h -= 1.0;
            }
        }

        // --

        return new(
            h * 360.0,
            s * 100.0,
            l * 100.0,
            rgb.Alpha);
    }

    public static RgbColor HsbToRgb(
        HsbColor hsb)
    {
        double red = 0, green = 0, blue = 0;

        double h = hsb.Hue;
        var s = (double)hsb.Saturation / 100;
        var b = (double)hsb.Brightness / 100;

        if (Math.Abs(s - 0) < 0.00001)
        {
            red = b;
            green = b;
            blue = b;
        }
        else
        {
            // the color wheel has six sectors.

            var sectorPosition = h / 60;
            var sectorNumber = (int)Math.Floor(sectorPosition);
            var fractionalSector = sectorPosition - sectorNumber;

            var p = b * (1 - s);
            var q = b * (1 - s * fractionalSector);
            var t = b * (1 - s * (1 - fractionalSector));

            // Assign the fractional colors to r, g, and b
            // based on the sector the angle is in.
            switch (sectorNumber)
            {
                case 0:
                    red = b;
                    green = t;
                    blue = p;
                    break;

                case 1:
                    red = q;
                    green = b;
                    blue = p;
                    break;

                case 2:
                    red = p;
                    green = b;
                    blue = t;
                    break;

                case 3:
                    red = p;
                    green = q;
                    blue = b;
                    break;

                case 4:
                    red = t;
                    green = p;
                    blue = b;
                    break;

                case 5:
                    red = b;
                    green = p;
                    blue = q;
                    break;
            }
        }

        var nRed = Convert.ToInt32(red * 255);
        var nGreen = Convert.ToInt32(green * 255);
        var nBlue = Convert.ToInt32(blue * 255);

        return new(nRed, nGreen, nBlue, hsb.Alpha);
    }

    public static RgbColor HslToRgb(
        HslColor hsl)
    {
        double red, green, blue;

        var h = hsl.PreciseHue / 360.0;
        var s = hsl.PreciseSaturation / 100.0;
        var l = hsl.PreciseLight / 100.0;

        if (Math.Abs(s - 0.0) < 0.00001)
        {
            red = l;
            green = l;
            blue = l;
        }
        else
        {
            double var2;

            if (l < 0.5)
            {
                var2 = l * (1.0 + s);
            }
            else
            {
                var2 = l + s - s * l;
            }

            var var1 = 2.0 * l - var2;

            red = hue2Rgb(var1, var2, h + 1.0 / 3.0);
            green = hue2Rgb(var1, var2, h);
            blue = hue2Rgb(var1, var2, h - 1.0 / 3.0);
        }

        // --

        var nRed = Convert.ToInt32(red * 255.0);
        var nGreen = Convert.ToInt32(green * 255.0);
        var nBlue = Convert.ToInt32(blue * 255.0);

        return new(nRed, nGreen, nBlue, hsl.Alpha);
    }

    private static double hue2Rgb(
        double v1,
        double v2,
        double vH)
    {
        if (vH < 0.0)
        {
            vH += 1.0;
        }
        if (vH > 1.0)
        {
            vH -= 1.0;
        }
        if (6.0 * vH < 1.0)
        {
            return v1 + (v2 - v1) * 6.0 * vH;
        }
        if (2.0 * vH < 1.0)
        {
            return v2;
        }
        if (3.0 * vH < 2.0)
        {
            return v1 + (v2 - v1) * (2.0 / 3.0 - vH) * 6.0;
        }

        return v1;
    }

    /// <summary>
    /// Determines the maximum value of all of the numbers provided in the
    /// variable argument list.
    /// </summary>
    private static double getMaximumValue(
        params double[] values)
    {
        var maxValue = values[0];

        if (values.Length >= 2)
        {
            for (var i = 1; i < values.Length; i++)
            {
                var num = values[i];
                maxValue = Math.Max(maxValue, num);
            }
        }

        return maxValue;
    }

    /// <summary>
    /// Determines the minimum value of all of the numbers provided in the
    /// variable argument list.
    /// </summary>
    private static double getMinimumValue(
        params double[] values)
    {
        var minValue = values[0];

        if (values.Length >= 2)
        {
            for (var i = 1; i < values.Length; i++)
            {
                var num = values[i];
                minValue = Math.Min(minValue, num);
            }
        }

        return minValue;
    }
}

Directory.Build.props

<Project>
 <PropertyGroup>
   <LangVersion>preview</LangVersion>
 </PropertyGroup>
</Project>

HsbColor.cs

namespace ZetaColorEditor.Colors;

using System.Drawing;

/// <summary>
/// Represents a HSV (=HSB) color space.
/// http://en.wikipedia.org/wiki/HSV_color_space
/// </summary>
[PublicAPI]
public sealed class HsbColor(double hue,
	double saturation,
	double brightness,
	int alpha)
{
	/// <summary>
    /// Gets or sets the hue. Values from 0 to 360.
    /// </summary>
    public double PreciseHue { get; } = hue;

    /// <summary>
    /// Gets or sets the saturation. Values from 0 to 100.
    /// </summary>
    public double PreciseSaturation { get; } = saturation;

    /// <summary>
    /// Gets or sets the brightness. Values from 0 to 100.
    /// </summary>
    public double PreciseBrightness { get; } = brightness;

    public int Hue => Convert.ToInt32(PreciseHue);

    public int Saturation => Convert.ToInt32(PreciseSaturation);

    public int Brightness => Convert.ToInt32(PreciseBrightness);

    /// <summary>
    /// Gets or sets the alpha. Values from 0 to 255.
    /// </summary>
    public int Alpha { get; } = alpha;

    public static HsbColor FromColor(
        Color color)
    {
        return ColorConverting.ColorToRgb(color).ToHsbColor();
    }

    public static HsbColor FromRgbColor(
        RgbColor color)
    {
        return color.ToHsbColor();
    }

    public static HsbColor FromHsbColor(
        HsbColor color)
    {
        return new(color.PreciseHue, color.PreciseSaturation, color.PreciseBrightness, color.Alpha);
    }

    public static HsbColor FromHslColor(
        HslColor color)
    {
        return FromRgbColor(color.ToRgbColor());
    }

    public override string? ToString()
    {
        return $@"Hue: {Hue}; saturation: {Saturation}; brightness: {Brightness}.";
    }

    public Color ToColor()
    {
        return ColorConverting.HsbToRgb(this).ToColor();
    }

    public RgbColor ToRgbColor()
    {
        return ColorConverting.HsbToRgb(this);
    }

    public HsbColor ToHsbColor()
    {
        return new(PreciseHue, PreciseSaturation, PreciseBrightness, Alpha);
    }

    public HslColor ToHslColor()
    {
        return ColorConverting.RgbToHsl(ToRgbColor());
    }

    public override bool Equals(object? obj)
    {
        var equal = false;

        if (obj is HsbColor color)
        {
	        if (Math.Abs(PreciseHue - color.PreciseHue) < 0.00001 &&
	            Math.Abs(PreciseSaturation - color.PreciseSaturation) < 0.00001 &&
	            Math.Abs(PreciseBrightness - color.PreciseBrightness) < 0.00001 &&
	            Alpha == color.Alpha)
            {
                equal = true;
            }
        }

        return equal;
    }

    public override int GetHashCode()
    {
        return $@"H:{Hue}-S:{Saturation}-B:{Brightness}-A:{Alpha}".GetHashCode();
    }
}

HslColor.cs

namespace ZetaColorEditor.Colors;

using System.Drawing;

/// <summary>
/// Represents a HSL color space.
/// http://en.wikipedia.org/wiki/HSV_color_space
/// </summary>
[PublicAPI]
public sealed class HslColor(
	double hue,
	double saturation,
	double light,
	int alpha)
{
	/// <summary>
	/// Gets the hue. Values from 0 to 360.
	/// </summary>
	public int Hue => Convert.ToInt32(PreciseHue);

	/// <summary>
	/// Gets the precise hue. Values from 0 to 360.
	/// </summary>
	public double PreciseHue { get; } = hue;

	/// <summary>
	/// Gets the saturation. Values from 0 to 100.
	/// </summary>
	public int Saturation => Convert.ToInt32(PreciseSaturation);

	/// <summary>
	/// Gets the precise saturation. Values from 0 to 100.
	/// </summary>
	public double PreciseSaturation { get; } = saturation;

	/// <summary>
	/// Gets the light. Values from 0 to 100.
	/// </summary>
	public int Light => Convert.ToInt32(PreciseLight);

	/// <summary>
	/// Gets the precise light. Values from 0 to 100.
	/// </summary>
	public double PreciseLight { get; } = light;

	/// <summary>
	/// Gets the alpha. Values from 0 to 255
	/// </summary>
	public int Alpha { get; } = alpha;

	public static HslColor FromColor(Color color)
	{
		return ColorConverting.RgbToHsl(ColorConverting.ColorToRgb(color));
	}

	public static HslColor FromRgbColor(RgbColor color)
	{
		return color.ToHslColor();
	}

	public static HslColor FromHslColor(HslColor color)
	{
		return new(
			color.PreciseHue,
			color.PreciseSaturation,
			color.PreciseLight,
			color.Alpha);
	}

	public static HslColor FromHsbColor(HsbColor color)
	{
		return FromRgbColor(color.ToRgbColor());
	}

	public override string? ToString()
	{
		return Alpha < 255
			? $@"hsla({Hue}, {Saturation}%, {Light}%, {Alpha / 255f})"
			: $@"hsl({Hue}, {Saturation}%, {Light}%)";
	}

	public Color ToColor()
	{
		return ColorConverting.HslToRgb(this).ToColor();
	}

	public RgbColor ToRgbColor()
	{
		return ColorConverting.HslToRgb(this);
	}

	public HslColor ToHslColor()
	{
		return this;
	}

	public HsbColor ToHsbColor()
	{
		return ColorConverting.RgbToHsb(ToRgbColor());
	}

	public override bool Equals(object? obj)
	{
		var equal = false;

		if (obj is HslColor color)
		{
			if (Math.Abs(Hue - color.PreciseHue) < 0.00001 &&
				Math.Abs(Saturation - color.PreciseSaturation) < 0.00001 &&
				Math.Abs(Light - color.PreciseLight) < 0.00001 &&
				Alpha == color.Alpha)
			{
				equal = true;
			}
		}

		return equal;
	}

	public override int GetHashCode()
	{
		return $@"H:{PreciseHue}-S:{PreciseSaturation}-L:{PreciseLight}-A:{Alpha}".GetHashCode();
	}
}

RgbColor.cs

namespace ZetaColorEditor.Colors;

using System.Drawing;

/// <summary>
/// Represents a RGB color space.
/// http://en.wikipedia.org/wiki/HSV_color_space
/// </summary>
[PublicAPI]
public sealed class RgbColor(
	int red,
	int green,
	int blue,
	int alpha)
{
	/// <summary>
	/// Gets or sets the red component. Values from 0 to 255.
	/// </summary>
	public int Red { get; } = red;

	/// <summary>
	/// Gets or sets the green component. Values from 0 to 255.
	/// </summary>
	public int Green { get; } = green;

	/// <summary>
	/// Gets or sets the blue component. Values from 0 to 255.
	/// </summary>
	public int Blue { get; } = blue;

	/// <summary>
	/// Gets or sets the alpha component. Values from 0 to 255.
	/// </summary>
	public int Alpha { get; } = alpha;

	public static RgbColor FromColor(
		Color color)
	{
		return ColorConverting.ColorToRgb(color);
	}

	public static RgbColor FromRgbColor(
		RgbColor color)
	{
		return new(color.Red, color.Green, color.Blue, color.Alpha);
	}

	public static RgbColor FromHsbColor(
		HsbColor color)
	{
		return color.ToRgbColor();
	}

	public static RgbColor FromHslColor(
		HslColor color)
	{
		return color.ToRgbColor();
	}

	public override string? ToString()
	{
		return Alpha < 255 ? $@"rgba({Red}, {Green}, {Blue}, {Alpha / 255d})" : $@"rgb({Red}, {Green}, {Blue})";
	}

	public Color ToColor()
	{
		return ColorConverting.RgbToColor(this);
	}

	public RgbColor ToRgbColor()
	{
		return this;
	}

	public HsbColor ToHsbColor()
	{
		return ColorConverting.RgbToHsb(this);
	}

	public HslColor ToHslColor()
	{
		return ColorConverting.RgbToHsl(this);
	}

	public override bool Equals(object? obj)
	{
		var equal = false;

		if (obj is RgbColor color)
		{
			if (Red == color.Red && Blue == color.Blue && Green == color.Green && Alpha == color.Alpha)
			{
				equal = true;
			}
		}

		return equal;
	}

	public override int GetHashCode()
	{
		return $@"R:{Red}-G:{Green}-B:{Blue}-A:{Alpha}".GetHashCode();
	}
}

It has been long since I last touched this, but I finally had some time to make the code public. Will probably turn it into a nuget package later.

I like it very much, thank you, @hacklex.