ColorConversions.cs

private static float Hue2Rgb(float p, float q, float t)
{
    if (t < 0) t += 1;
    if (t > 1) t -= 1;
    if (t < 1.0 / 6.0) return p + (q - p) * 6.0f * t;
    if (t < 1.0 / 2.0) return q;
    if (t < 2.0 / 3.0) return p + (q - p) * (2.0f / 3.0f - t) * 6.0f;
    return p;
}

public static BGRAColor FromHsv(HsvColor color)
{
    float r = 0;
    float g = 0;
    float b = 0;

    var i = (float)Math.Floor(color.Hue * 6f);
    var f = color.Hue * 6f - i;
    var p = color.Value * (1f - color.Saturation);
    var q = color.Value * (1f - f * color.Saturation);
    var t = color.Value * (1f - (1f - f) * color.Saturation);

    switch (i % 6)
    {
        case 0: r = color.Value; g = t; b = p; break;
        case 1: r = q; g = color.Value; b = p; break;
        case 2: r = p; g = color.Value; b = t; break;
        case 3: r = p; g = q; b = color.Value; break;
        case 4: r = t; g = p; b = color.Value; break;
        case 5: r = color.Value; g = p; b = q; break;
    }

    return new BGRAColor(Trim(r * 255), Trim(g * 255), Trim(b * 255), 255);
}

public static BGRAColor FromHsl(HslColor color)
{
    float r, g, b;

    if (color.Saturation == 0)
    {
        r = g = b = color.Lightness; // achromatic
    }
    else
    {
        var q = color.Lightness < 0.5 ? color.Lightness * (1 + color.Saturation) : color.Lightness + color.Saturation - color.Lightness * color.Saturation;
        var p = 2f * color.Lightness - q;
        r = Hue2Rgb(p, q, color.Hue + 1.0f / 3.0f);
        g = Hue2Rgb(p, q, color.Hue);
        b = Hue2Rgb(p, q, color.Hue - 1.0f / 3.0f);
    }

    return new BGRAColor(Trim(r * 255), Trim(g * 255), Trim(b * 255), 255);
}

public static HslColor RgbToHsl (this IColor color)
{
    var r = color.R / 255.0f;
    var g = color.G / 255.0f;
    var b = color.B / 255.0f;
    var max = Math.Max(r, Math.Max(g, b));
    var min = Math.Min(r, Math.Min(g, b));

    float h,s,l;
    h = s = l = (max + min) / 2;

    if (max == min)
    {
        h = s = 0; // achromatic
    }
    else
    {
        var d = max - min;
        s = l > 0.5 ? d / (2 - max - min) : d / (max + min);

        if(max == r)
        {
            h = (g - b) / d + (g < b ? 6 : 0);
        }
        else if(max == g)
        {
            h = (b - r) / d + 2;
        }
        else if(max == b)
        {
            h = (r - g) / d + 4;
        }

        h /= 6;
    }

    return new HslColor { Hue = h, Saturation = s, Lightness = l };
}

public static HsvColor RgbToHsv(this IColor color)
{
    var r = color.R / 255.0f;
    var g = color.G / 255.0f;
    var b = color.B / 255.0f;
    var max = Math.Max(r, Math.Max(g, b));
    var min = Math.Min(r, Math.Min(g, b));

    float h, s, v;
    h = s = v = max;

    var d = max - min;
    s = max == 0 ? 0 : d / max;

    if (max == min)
    {
        h = 0; // achromatic
    }
    else
    {
        if(max == r)
        {
            h = (g - b) / d + (g < b ? 6 : 0);
        }
        else if (max == g)
        {
            h = (b - r) / d + 2;
        }
        else if (max == b)
        {
            h = (r - g) / d + 4;
        }

        h /= 6;
    }

    return new HsvColor { Hue = h, Saturation = s, Value = v };
}

static float RGBChannelFromHue(float m1, float m2, float h)
{
    h = (h + 1f) % 1f;
    if (h < 0) h += 1;
    if (h * 6 < 1) return m1 + (m2 - m1) * 6 * h;
    else if (h * 2 < 1) return m2;
    else if (h * 3 < 2) return m1 + (m2 - m1) * 6 * (2f / 3f - h);
    else return m1;
}