Once you move in you can decorate the place any way you want (unless that involves breaking through walls, I think that should require a landlord’s permission). BUT you have to restore everything to the way it was once you move out, i.e. if the apartment was wallpapered and painted white that’s the way you have to leave it. HOWEVER again, German “rental law” (or whatever you might call it) is tricky business, as there often are changes on what is a reasonable demand of the landlord. That’s why it’s recommendable to get legal insurance before you move out, just in case you have to take a lawyer interpreting all those clauses in your rental contract you never thought could hold so many different meanings.
Well, the landlord has a say insofar as they get to inspect the place before you move out and say yay or nay - in the “nay” case you get the opportunity to improve on your decorating efforts. If not successful, the landlord will keep your deposit. Usually, though, things go without a hitch since both parties have an interest that the apartment will transfer smoothly.
Only occasionally you’ll run into trouble - then the tenant will swear the landlord is out to screw them out of their deposit and the landlord will moan that the tenants have run down his precious property (which might both be true). That’s where the legal insurance steps in and you go to court - otherwise as a tenant you’re pretty much SOL as most landlords tend to have more money, hence more leverage. (I’m not saying that there are no tenants who DO run down the property, just from Quasi 's potential future tenant point of view, the legal insurance bit might be more relevant).
