World building/Sky Color
The sky doesn't HAVE to be blue. It can be different. A few examples of causes:
Dust or gases in the air
Distance from light (The farther away the colder and darker the color)
Atmosphere Thickness (Theories may be conflicting)
The sky can even end up red. But, this will have effects on evolution, climate, inhabitants, and more. Breathing and Lifespan can be affected. Chances of disaster can be changed, too. Another reason is the type of star. O-type stars emit very purple light and are short lived, M-type red dwarf stars have reddish light, and all other stars in 400-40 nm range, like our star, have blue-purple lights. Most skies will be purple or blue. This can effect water, moon, cloud, and more appearances, change camouflage, plant colors, religion and etc. Other things can still affect these, like ground or soil type, so be careful.