runtime: System.Drawing.Color is possibly missing 8 colors

Background and Motivation

It appears that the System.Drawing.Color names are intended to track the CSS color names; if that is correct, there are some colors which need to be added. Two reasons for thinking the names are supposed to track CSS colors are:

• The Documentation for System.Drawing.Color says “For more information about these colors, see Colors by Name.” which links to Mozilla’s documentation on CSS color names.

• Pull Request https://github.com/dotnet/corefx/pull/41561 where one of the color values differed from the CSS value, and the .Net color value was changed to agree with CSS.

Proposed API

Affecting at least KnownColor.cs and KnownColorNames.cs and KnownColorTable.cs and Affecting at least Color.cs, the significant differences are the addition of the new RebeccaPurple color, and the variant spellings of grAy colors as grEy:

namespace System.Drawing
{
    enum KnownColor
    {
+    RebeccaPurple,
+    DarkGrey,
+    DarkSlateGrey,
+    DimGrey,
+    Grey,
+    LightGrey,
+    LightSlateGrey,
+    SlateGrey,
     }

    public readonly struct Color : IEquatable<Color>
    {
+    public static Color RebeccaPurple;
+    public static Color DarkGrey;
+    public static Color DarkSlateGrey;
+    public static Color DimGrey;
+    public static Color Grey;
+    public static Color LightGrey;
+    public static Color LightSlateGrey;
+    public static Color SlateGrey;
    }
}

Possibly related, System.Windows.Media.Colors

Usage Examples

using System.Drawing;

string text = String.Format(
    "The CSS color 'RebeccaPurple' has Red component of {0}", 
    Color.RebeccaPurple.R);

Alternative Designs

I have not considered any particular designs, only intending to report this as a bug where the existing behaviour differs from the intended behaviour.

Risks

This will change the total number of items in the Color enum, and (depending on whether the new ones are added in order, or to the end) might change the existing color locations.

---

I think the missing color values are:

• RebeccaPurple #663399
• DarkGrey #a9a9a9
• DarkSlateGrey #2f4f4f
• DimGrey #696969
• Grey #808080
• LightGrey #d3d3d3
• LightSlateGrey #778899
• SlateGrey #708090