I'm not really sure if this is feasible or practical to implement, and it's definitely not needed in the game for any gameplay purposes, but it would be a really cool effect if it's possible. It would be cool if the sides of planets not facing a star would be dark, like in real life. On unsettled planets they could be completely dark and on settled planets they could be covered in lights. The density of the lights could depend on the population of the planet. Just an idea...