Time of day?

[Kill_All_Monkeys]

So when me and my friends started a game in Slums the other day, I noticed the sky appeared to be a nice and simple sunset with orange as the prominent color. Then I remembered when I had been playing in Slums earlier that day I recalled seeing a bright, blue sunny backdrop instead of an orange sunset.

So is this common knowledge that just simply eluded me this whole time? Or do some of the maps have different variants as in the time of day they take place in?