If you're colour blind, you may have difficulty getting a class 2 medical, which is required for a PPL, much less a class 1 (required for a commercial). Given your suspicions, I would strongly suggest getting the medical done BEFORE you start any flight training - it doesn't cost a lot, and there is an AME at Wycombe Air Park (Dr. Tobias, if I remember correctly); you'll need to get one done before you go solo on the PPL anyway, so you're not spending any money you wouldn't have to spend in due course, and it might save you investing in an impossible license.