Check out http://meta.stackoverflow.com/q/107246/189958https://meta.stackoverflow.com/q/107246/189958
Pertinent answer quoted below...
Short answer: you can ask for anything you want, as long as it doesn't interfere with functionality.
Each graduating site gets its own unique design theme created by Stack Exchange's professional in-house design team (currently Jin), working with other designers as needed.
So far, every site's theme has included
- a custom logo and favicon custom decorative graphics (or intentional lack thereof)
- a consistent color scheme
Most sites have also received
- unique fonts consistent with the site theme
- decorative boxes and borders consistent with the site theme
- themed badge shapes/sizes/colors (color referring to background color, not bronze/silver/gold)
- themed tag shapes/sizes/colors
- unique upvote/downvote/favorite button images
Some sites have other changes that have to do with their topics. Photography's top bar is organized differently to make room for a "featured photo." Unix and Linux has slashes prepended to the text of its header buttons to give the feel that those link to "subdirectories" of the site. And Apple's markup looks like an Apple keyboard's key.