These two could overlap, but there is a difference. Works for me = it works, in my opinion; I like it. This is the usual meaning. It would be more likely for a person to say it about themselves, not about another person. It works on you = That piece of clothing looks good on you. If I said "It works for you." I would probably be saying, that looks good on you, but not on other people. I probably wouldn't say it, because it might be interpreted as meaning "You like that." You usually don't tell a person what they like and don't like. Another meaning: Somebody works on you = somebody is trying to convince you of something you don't agree with yet. [I don't think that is what it means here]