Why does this color comparison fail?

Question

Why does this assertion fail?

Assert.AreEqual( Color.Red, Color.FromArgb( Color.Red.A, Color.Red.R, Color.Red.G, Color.Red.B ) );

Answer 1

Here is how Colors comparison implemented:

public override bool Equals(object obj)
{
    if (obj is Color)
    {
        Color color = (Color) obj;
        if ((this.value == color.value)
            && (this.state == color.state)
            && (this.knownColor == color.knownColor))
        {
            return ((this.name == color.name)
                || ((this.name != null)
                   && (color.name != null)
                   && this.name.Equals(color.name)));
        }
    }
    return false;
}

How it works:

1. Field value compared. It is Argb values of current instance (they are stored in one field of type long). So, if Argb different, we have different colors. You pass this step successfully.
2. Field state compared. It shows the way how color was created: from Argb, from KnownColor, or by name. Actually your comparison fails on this step.
3. Field knownColor compared. It has value of KnownColor enum, or zero, if color was not created from known color.
4. Field name compared. It has null value for all colors except ones created by name.

So, if you want to compare values of colors, you should use value field in comparison (it is returned by ToArgb method):

Assert.AreEqual(color1.ToArgb(), color2.ToArgb());

Edit

To create copy of some color you can use following extension method:

public static class ColorHelper
{
    public static Color Copy(this Color color)
    {
        if (color.IsKnownColor)
            return Color.FromKnownColor(color.ToKnownColor());

        if (color.IsNamedColor)
            return Color.FromName(color.Name);

        // this is better, then pass A,r,g,b separately
        return Color.FromArgb(color.ToArgb()); 
    }

Now assertion passes:

Assert.AreEqual(Color.Red, Color.Red.Copy());

But it makes no sense, because you can use single color instance in every place of your program :)

Answer 2

Color.Red is a named color, while Color.FromArgb(...) is not. So they're not considered equal, even though they have the same ARGB values. Note that the string representation is also different:

Color.Red.ToString()           : "Color [Red]"
Color.FromArgb(...).ToString() : "Color [A=255, R=255, G=0, B=0]"