Force specific background color for a specific user??

So I was browsing the web, looking for a way to disable the Start background for a certain user (he keeps toying around with windows 8) and other permissions too. Most things I disabled were meant to be used with gpedit.exe, but I used a user Snap-In in mmc.exe. However, I and some other people want to change the background. So how do I disable this setting for a specific user?

It's been a week and no answer...