that's normal its just shading to give impression of illumination
I'm a Trimbler now!
Well, that's just because of the shading I guess. Basically (if you have problems with face orientation), just set the two kinds of faces to something strikingly different. I think Dave uses some irritating magenta or what so that he cannot bear it too long and reverses back faces quickly.
Ok, great, thanks, that's what I thought (SketchUp is trying to replicate the effects of light).