We had white gravel up until a week ago, honestly the most stupid idea I've ever had. Snails didn't clean it, plecs didn't clean it and it turned beige. That was despite regular gravel vacs and two full substrate cleaning. Switched to sand because we have corydoras and the tank honestly has never looked cleaner even after a week of plec poo. Trying to keep that gravel white is gonna be a headache, so I'd say either swap it for something else (sand or darker colour gravel) or learn to love the colour beige ;-)