Acid stains were used commonly in the past, but they are not environmentally safe. They have been almost entirely replaced by dyes. These dyes are mixed with a carrier, such as an alcohol and sprayed onto concrete. It's topped with a water-based sealer to create the mottled look, accentuating the unique characteristics of the concrete.
Mask off all walls and trim molding with tape and plastic sheeting. Painter's tape will protect the wall finish without damaging it during removal, but it can peel off the surface if exposed to the dye solution. Place masking tape over the painter's tape to hold the plastic sheeting in place.