I'm building a base and attempting to paint background blocks I've placed. Smooth wall panels like those that come with the human ship in particular. For some reason a few I placed were paint-able and some weren't. After some thorough testing I determined that I'm unable to paint a background block that hasn't had a foreground block ontop of it before. I can get by via placing a block on top, painting the stack, and removing the foreground block... but it's unnecessarily tedious.