SK...there are 18 colors in Control Panel.I think its the color between 12 and 13.(thats missing)
Fixed and new colors added to the Task Dialog Buttons (also edited wiki page)
If you do have a specific problem then your best bet is to e-mail me directly.
I got to agree with IR, we ALL want to know... if you know what these colors are please by all means fill us in on the ones we are missing :/