on this site that has had good luck painting ceramic tiles. I would never even consider it as I have seen too many bathrooms that did not go well. You do have to use a expensive epoxy mixture paint.
Where I have been commissioned to tear out the tile and re tile with a up dated color and style. the existing tile had been painted with that same expoxy, but the paint seemed to peel at the grout line and seemed to hold on the ceramic glaze area, but not on the grout.