I learned that if you spray paint the inside of a model black it will prevent coaches from glowing. You can then paint over the black paint with original color.
True but if you ever decide to add an interior, you’re going to have to repaint the inside. If you paint the inside and outside of the car with any color it should block the light glowing thru. I use primer gray or a light green (light green was very common interior color for passenger cars, cabooses, depots etc.) and then spray the exterior color (like Pullman green). I put a folded soft paper towel inside the model so the inside remains the lighter color.