Pia as long as you have some paint left over from the walls you can do emergency touch ups as and when the finish starts to look a little dodgy so as a short term freshener it should be OK.
Please, please do not paint the tiles with ordinary paint. The ceramic finish on the tiles will not allow the paint to adhere properly and you will end up with peeling paint very quickly. To get a halfway decent finish on the tiles you really have to use some form of specialist primer. I have had people on the phone in tears wanting my husband to come out and make their bathrooms look less like a slum after they had painted their tiles "like they do on Telly"
Before you go any where near the tiles with paint try giving the grout between them a real going over with bleach and an old toothbrush. You could then use a
'Grout Pen' which will really whiten the grout and make the tiling look a lot fresher.
Jo
