floor or wall grout sanded or non sanded. wall grout it would be just as easy to scrape with grout removal tool and regrout with desired color.floor grout is tougher and would be time consuming but the same process sould be used as most grouts today have sealers in them already. another alternative is to get a comercial type grout cleaner and clean the grout but follow directions
As stated in one of the responses, muriatic acid can be dangerous, so you may want to try something safer if you really just want the grout to look white again. If so, try SNAP Cream Scouring Cleanser from our 'Home Care Store' at www.shopEZ.unfranchise.com. If you want to use the Muriactic Acid, you should check out ClearShield from the 'Personal Care Store' at www.shopEZ.unfranchise.com. This product is used in our lab at work to protect people from caustic acids, muriatic acid, sulfuric acid, etc. I've someone demonstrate it by pouring muriactic acid on his hands while holding tin foil. The tin foil disintegrated and his hands were fine! Still be careful and use as directed. Good luck.