Yes, you can paint tiles, but that was not always the case. Tiles are so glossy that no paint available can adhere to the surface. However, by using a relatively new super-adherent primer that will, as the name suggests, adhere to difficult surfaces, you can then apply any kind of paint over that. You should be warned that no paint will last forever in the shower area. You will have to repeat the process over time. The ideal paint to apply over the super-adherent primer is a latex-and-acrylic combination paint. It is very durable and can withstand scrubbing without suffering any damage. There are several super-adherent primers on the market. You want one that is specifically designed for ceramic tiles.