I am not sure if you are talking about the outside or the inside. But I'll just drop my two cents here, because I never had inspiration problems with colour.
INSIDE
If you own your place, or if you are willing to repaint all walls before you leave (or you have a nice landlord, like I had, who thought my red wall was awesome), you can change the interior design of your home at will.
To buy colours, you can go to Hornbach, Bauhaus, Jumbo, etc. They will only have a couple of colours out (the 9010, and perhaps the lila and the green which is now fashion for little kids rooms). However, you can bring them your
RAL or
NCS reference and they will produce the colour in loco.
If you are looking for wallpaper, you will have a little more difficult to find something decent on the medium and lower price range. You will, however, find gorgeous patterns on expensive designer shops. But there is this fantastic thing called internet and you can order
wallpaper of all shapes and colours. I bought mine when I went to visit my parents - my home country is going through a DIY craze at the moment. You can drop to France for the relatively cheap and decent
Leroy Merlin.
OUTSIDE
The city does not decide which colours to use on a specific house. The architect does. However, there are some guidelines to specific areas - when it's a protected city center, for example, you might be able to only use ocre tones because that is the traditional palette used. Or that jalousies should be on a green-to-blue tone. Between green and blue there are quite a few tones, though. And ocre goes from yellow to red.
When you, as an individual home owner, go to the city chamber to say you'd like to change the colour of your facade to lime green, they might block you immediately. I got to learn from my profession and experience that choosing colours for a house doesn't only need a good eye, but negotiation skills akin to NATO officers... And that playing the "architect card" sometimes does wonders.
All that pertains the outside of your home will probably need a permit and approval from the city chamber, but with enough negotiation, you might be able to use that fluorescent green you always dreamed about

On the other hand, if the city refuses to allow your desired colour, the options are quite large - a small percentage change on the values can make a completely different tone.
P.S.: Unfortunately, yes, the mean idiot, for lack of a better word, does exist on the city chamber that refuses something for ridiculous or no reasons at all. But you can try to go over him by asking a committee meeting to present your case. I recently had a case like that - when the other guys in the committee heard our troubles, they looked at the guy with a "what the hell, dude?" look and let us do what we wanted.