Painting in mobile app

I see the paint brush icon and how to switch between different paint schemes. I see how to alter the default colors and to use the custom setting but I'm not seeing a way to paint an individual part without the whole rocket turning that color. Is this possible on the mobile app or do we just have these presets so far? What I'm trying to do is paint on stage one color and the interstage another and possibly other parts like the nose cone a separate color. Thanks for any help.