Dado’s Masterclass is by far the best. You can purchase individual modules or the whole certificate course which will turn you into a professional colorist. He’s a good mentor who cares about and actively pushes student progress. Definitely stay away from Waqas Qazi and his partner Marieta Farfarova, they are unprofessional hacks who sell overpriced, mostly useless and often outrageously absurd ‘secret sauces’ that help no one.