How to get the name of color while having its RGB value in C#?

As noted in comments, the KnownColor enumeration can be used to make this simpler:

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Reflection;

class Test
{
    static void Main()
    {
        Color color = Color.FromArgb(255, 0, 0);
        Console.WriteLine(color.Name); // ffff0000

        var colorLookup = Enum.GetValues(typeof(KnownColor))
               .Cast<KnownColor>()
               .Select(Color.FromKnownColor)
               .ToLookup(c => c.ToArgb());

        // There are some colours with multiple entries...
        foreach (var namedColor in colorLookup[color.ToArgb()])
        {
            Console.WriteLine(namedColor.Name);
        }
    }
}

---

Original answer

Color.FromArgb will give you a Color, but it will never have a name. You need to use reflection to get the named colours, as far as I’m aware.

Here’s another version of Cole Campbell’s solution which I was working up at the same time…

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Reflection;

class Test
{
    static void Main()
    {
        Color color = Color.FromArgb(255, 0, 0);
        Console.WriteLine(color.Name); // ffff0000

        var colorLookup = typeof(Color)
               .GetProperties(BindingFlags.Public | BindingFlags.Static)
               .Select(f => (Color) f.GetValue(null, null))
               .Where(c => c.IsNamedColor)
               .ToLookup(c => c.ToArgb());

        // There are some colours with multiple entries...
        foreach (var namedColor in colorLookup[color.ToArgb()])
        {
            Console.WriteLine(namedColor.Name);
        }
    }
}