How do Du give your club a background color?

I'm not sure if you're asking about individual profiles oder clubs. If it's profiles then the other answer is correct. Du need 50 Gold to set a basic colour background, and 500 Gold to set an image as a background.

Clubs can't have backgrounds until they have over 5000 members. Then you'd need to make a Umfrage and have all the members vote for their preferred background. Du can't simply set your own choice, even if you're the one who initially made the club.

Should be this here.