Why does Color.IsNamedColor not work when I create a color using Color.FromArgb()?

Question

In my app I allow the user to build a color, and then show him the name or value of the color later on. If the user picks red (full red, not red-ish), I want to show him "red". If he picks some strange color, then the hex value would be just fine. Here's sample code that demonstrates the problem:

static string GetName(int r, int g, int b)
{
    Color c = Color.FromArgb(r, g, b);  // Note that specifying a = 255 doesn't make a difference
    if (c.IsNamedColor)
    {
        return c.Name;
    }
    else
    {
        // return hex value
    }
}

Even with very obvious colors like red IsNamedColor never returns true. Looking at the ARGB values for my color and Color.Red, I see no difference. However, calling Color.Red.GetHashCode() returns a different hash code than Color.FromArgb(255, 0, 0).GetHashCode().

How can I create a color using user specified RGB values and have the Name property come out right?

Answer 1

From MSDN.

Property Value Type: System.Boolean
true if this Color was created by using either the FromName method or the FromKnownColor method; otherwise, false.

You could build a map from all KnownColors rgb tuples to names I suppose.

Answer 2

This probably isn't the fastest method, but it does work. Colors don't have to match exactly for the name to be chosen e.g. GetColorName(Color.FromArgb(254, 254, 0)); will still return Yellow.

I've deliberately left out access modifiers

Color[] KnownColors; 

void Init (){
    KnownColors = (from colorInfo in typeof(Color).GetProperties(BindingFlags.Static | BindingFlags.CreateInstance |BindingFlags.Public)
                   where colorInfo.PropertyType == typeof (Color)
                   select (Color)colorInfo.GetValue(null, null)).Where (c => c.A != 0).ToArray();
}

string GetColorName(Color inColour)
{

    // I'm just getting started on LINQ so im not
    // sure how to do this with it (Maybe some one can help out with that)

    int MinDistance = int.MaxValue;

    Color closestKnown = Color.Black;
    foreach (var c in KnownColors)
    {
        var d = ColorDistance(c, inColour);

        if (d < MinDistance){
            closestKnown = c;
            MinDistance = d;
        }
    }

    return closestKnown.Name;
}


int ColorDistance(Color c1, Color c2)
    {

    var ad = (c1.A - c2.A);
    var rd = (c1.R - c2.R);
    var gd = (c1.G - c2.G);
    var bd = (c1.B - c2.B);

    return (ad * ad) + (rd * rd) + (gd * gd) + (bd * bd);
}