I have braces but i have the "clear" bands which turn yellow, what is the peroxide that can change them back?

The bands turn yellow after a few days because of the spices and oils in food. The orthodontist said that i can use peroxide to change them back to clear. He said that i should just gargle it in my mouth and spit it out but i don't know which peroxide he was talking about. Does anyone know? Thanks!