Preventing "glowing" buildings

[rlandry6]

Now that you know what's causing it, you can paint the inside with a dark color paint before you assemble the structure..

[MisterBeasley]

I've noticed even before putting some kits together that the walls don't block all the light. Once assembled with interior lighting, they will glow like the Chernobyl Valley Railroad. What's the best way to prevent this?