I am making a short story about terra forming mars. What colour would the plants and sky be if that were to happen? And what colour would a setting sun have?
Good answer Youtsay Igo but there were a few mistakes.
First if you are terraforming mars one of the key things to do would be to make the atmosphere bigger and more earth-like. Once you heat the planet and give it water you have all the elements done to give mars a blue sky with clouds.
Currently a sunset on mars is white but small amount of blues appear near the sun. However if the sky were to become blue...
This is an article from NASA about the color of plants
Both answers sound plausible to a reader and I would recommend just going with one of them and not do extensive research.
Color of the plants depends on the soil composition (mostly). While you would have to include large amounts of chlorophyll (green) if you want photosynthesis-enabled plants, the bark, fruit and flower colors would vary highly with soil composition. Mars has lots of iron dust which makes it look reddish. Iron compounds tend to have reddish-brown color so you may expect Martian plants to have a dun tint.
Sky color depends on auroras (magnetic field and intensity of charged particles) and composition of atmosphere. In the absence of an atmosphere (as of now) the sky would look a clear, bright white that would hurt the eyes in day time and an amazingly clear night sky where you would be able to see many more stars (and planets) than you see on earth.
Setting/rising sun is a difficult thing to say. No idea. It would definitely depend on the atmospheric composition but which gases result in which tint is unknown to me.