Before you start, try to think of a mood or atmosphere you’d like to create in the piece and then choose colours based off that. Do you want a sunlit golden look? Pastel and subdued? Rich and warm? Keep a particular eye on colour temperature and how it’s contrasted (or not) in the piece.
Since I assume you’re using a reference photo here, try to make sure the background colour you pick matches the lighting of the photo, because those colours have likely also affected your skin colour choices (as in ones skin reflects different tones depending on lighting), so the whole piece remains harmonious.