FindFriendlyColorName.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace lol
{
    public static class ColorHelpers
    {
        public static string GetColorName(Color c)
        {
            return FindClosestColorName(GetNamedColors(), c);
        }

        private static List<Tuple<string, Color>> GetNamedColors()
        {
            var colors = typeof(System.Drawing.Color).GetProperties();

            return Enum.GetValues(typeof(System.Drawing.KnownColor))
                .Cast<System.Drawing.KnownColor>()
                .Select(System.Drawing.Color.FromKnownColor)
                .Where(c => colors.Any(cc => cc.Name == c.Name))
                .Select(c => new Tuple<string, Color>(c.Name, c.ToAnnotationColor()))
                .ToList();
        }

        private static string FindClosestColorName(List<Tuple<string, Color>> colors, Color color)
        {
            var colorIdentity = color.GetColorIdentity();
            var colorsWithHueDistance = colors.Select(otherColor => new { Name = otherColor.Item1, Color = otherColor.Item2, Distance = Math.Abs(otherColor.Item2.GetColorIdentity() - colorIdentity) + otherColor.Item2.GetHueDistance(color) });
            var bestColor = colorsWithHueDistance.OrderBy(c => c.Distance);
            return bestColor.FirstOrDefault().Name;
        }
        
        // https://github.com/mono/mono/blob/master/mcs/class/System.Drawing/System.Drawing/Color.cs
        public float GetBrightness()
        {
            var minval = (byte) Math.Min(R, Math.Min(G, B));
            var maxval = (byte) Math.Max(R, Math.Max(G, B));
            return (float)(maxval + minval) / 510;
        }

        public float GetSaturation()
        {
            var minval = (byte)Math.Min(R, Math.Min(G, B));
            var maxval = (byte)Math.Max(R, Math.Max(G, B));

            if (maxval == minval)
                return 0.0f;

            int sum = maxval + minval;
            if (sum > 255)
                sum = 510 - sum;

            return (float)(maxval - minval) / sum;
        }

        public float GetHue()
        {
            var r = R;
            var g = G;
            var b = B;

            var minval = (byte)Math.Min(r, Math.Min(g, b));
            var maxval = (byte)Math.Max(r, Math.Max(g, b));

            if (maxval == minval)
            { 
                return 0.0f;
            }

            var diff = (float)(maxval - minval);
            var rnorm = (maxval - r) / diff;
            var gnorm = (maxval - g) / diff;
            var bnorm = (maxval - b) / diff;

            var hue = 0.0f;

            if (r == maxval)
            { 
                hue = 60.0f * (6.0f + bnorm - gnorm); 
            }

            if (g == maxval)
            { 
                hue = 60.0f * (2.0f + rnorm - bnorm);
            }

            if (b == maxval)
            { 
                hue = 60.0f * (4.0f + gnorm - rnorm);
            }

            if (hue > 360.0f)
            { 
                hue = hue - 360.0f;
            }

            return hue;
        }
    }
}