Should I quit band for AP studio art (Bad for college?)?

Even if you quit band, you can list those leadership positions on the app. Unless you plan to major in music of some kind, it shouldn't be too much of an issue. Take the art class if you want; you won't need to explain why you dropped band unless you apply somewhere that requires an interview (not all colleges require it, but they all encourage you to meet with an admissions counselor at some point) and they ask you about it.