Or you could
1. View any page of the forums where the color you want is shown
2. While the browser is open and that color is on the screen, press alt+prt src (next to scroll lock)
3. Open Photoshop
4. Create a new image, the resolution should already be set to almost your monitor size (if not, try step 1-2 again)
5. Now go to edit>paste and a perfect screenshot should appear
6. Use the eydropper and highlight the color you want
7. Paste it onto the black of your avatar
I say you just make it transparent