Getting paint off ceramic or porcelain tiles usually isn't that difficult, but getting it off grout is another matter. Grout is porous -- if it hasn't been sealed and the paint has a chance to penetrate, the process is akin to getting stain out of wood. If you've ever tried to do that, you know that you usually have to resort to the abrading action of sandpaper. The same is true for grout, but you can't approach the job in the same way. Start with tile-safe solvents, though, and progress to abrasives only if necessary. As a last resort, it's possible to cover the paint with different paint.
Paint Removal Procedure
Wipe up as much of the paint as you can while it's still wet, using a rag. If the spill is fresh and you get to it in time, you may avoid a lot of extra work by acting quickly. Wipe up the residue with an appropriate solvent -- soap and water for latex paint and mineral spirits for oil-based paint.
Remove dried oil paint using the same technique, but use mineral spirits as a solvent. If you don't have any luck, use acetone, kerosene or naphtha instead. As a last resort, try lacquer thinner. Test all of these solvents on the tiles before using them to make sure that they don't affect the finish.
Scrub out paint that has penetrated the grout using a battery-powered toothbrush. The soft bristles are to grout what sandpaper is to wood. Use it in conjunction with solvents, but beware -- some solvents, such as acetone and lacquer thinner, may dissolve the bristles.
In lieu of these solvents, make an abrasive paste of baking soda and water; apply it to the grout and scrub.
Use a citrus or soy-based paint stripper to remove large deposits of paint from tile and grout. Spread the stripper on the paint. Let it work for the time recommended on the container, and scrape off as much as you can with a plastic paint scraper. Use a toothbrush or 000 steel wool to get the stripper off the grout.
Color all the grout with an epoxy colorant as a last resort if you can't get the paint to come out. Before using this product, you need to clean the grout thoroughly with grout cleaner. Apply the colorant directly from the bottle and brush it in with a conventional toothbrush. It takes from 30 to 60 minutes to dry.