The Web Inspector is currently unable to show swatches that do not involve RGB or Hex values (IE: Black, White, Red, etc...).
I have created a patch that will allow it to render swatches for the 16 HTML and CSS standards defined colors: aqua, black, blue, fuchsia, gray, green, lime, maroon, navy, olive, purple, red, silver, teal, white, and yellow.
Created attachment 29249 [details]
Patch to allow 16 named colors
Allows 16 HTML/CSS colors to be background of swatches
Landed in r42224.