Our system methodically populates servers all over the world with your images to assure the fastest speed possible. Everywhere. This can take time to do, however. In some cases folks will see the chance immediately, and others it can be up to 2-3 hours to see changes. So give it a bit and you should see it pop up. :) This should only affect the banner and logo shown on the main forum page. You should, however, see the change to your logo colors reflected immediately on the login dialogue