I really like Vex Code, it works very well. Is there a way to program with black lettering on a white screen?
Not currently. In settings, it appears the corresponding setting is the editor theme. If you click the file drop down and select preferences, you get a settings page like the one below. But there is no way to change the editor theme. The existence of the little section suggests that eventually a light theme will be released (possibly with 1.0? no guarantees).