Topcolor doesn't work until you have 250 karma. A bug is currently displaying the setting even to users who don't have the karma to change it. Sorry! That's super annoying. We'll fix it.

Edit: it's fixed now, meaning that the setting is no longer displayed when it shouldn't be. Sorry for tantalizing.

Edit 2: I was looking for the post where pg first introduced the topcolor feature as a reward for karma, which I remember from years ago, but couldn't find it. If anybody can find it please let me know!