Note String Fret

The app I'm currently making has 3 types of question:
– what's the note?
– what's the fret?
– what's the string?

I've been spending a bit of time working out how to best visualise those classifications...would like to use colour but I think colour alone isn't enough. Trying out using some other information to reinforce those associations.

I don't think the stave for the note one is working out too well though...