Hi spr
I used tile paint to cover horrid green ones. Used white and I did have to coat it a few times to look good. However, have you considered using the transfers you can just slide on? I purchased a few packs of 6 transfers, then put them randomly on the tiles, and what a difference they made!
They look just as if they are painted on. Another thing you could try are stencils, which you can choose from a variety at DIY stores = then choose the little pots of paint especially for them, and get to work decorating as few or as many as you like!