What would influence skin color outside of stars and radiation? What sort of biology would allow for skintones of a wider color palette? [duplicate]

Question

The star is an F3.5 Main Sequence with a mass of 1.3 solar masses. The planet itself is 1.72 AU out from the star. The mass of the planet of about half the mass of Earth, while the Core Mass fraction remains the same as Earth (~35%). The radius of the planet is about 82% of Earth's (0.818 REarth). The Albedo is about the same as Earth's at 0.3, and the Greenhouse Effect is 1.7 to Earth's 1, so 70% stronger. This puts the surface temperatures average around 25 degrees Celcius. The atmospheric pressure is 1.8 to Earth's 1, 80% stronger, and the distribution of primary gases is the same as Earth in terms of composition, with the specifics being: Oxygen (27.5%), Carbon Dioxide (0.12%), Argon (0.92%), Nitrogen (71.45%). The atmospheric density is 2.152 kg/m^3. Gravity is about 75% of Earth's.

Not sure how important any of this specific information is, I'm new to this, so I figured I'd include what seemed fairly important when it came to this. The species for this hasn't been developed yet, but I intend for them to be around twice the height of humans and mammalian more than likely. I was mainly wondering how any of these factors would influence skin tone if anything might cause a particular change compared to human skin tones, and if other colors, such as red, blue, or anything else within the color wheel were even plausible as a skin tone.

Answer 1

The reduced color palette of mammals is an evolutionary accident

At some point in the early evolution of mammals, our distant ancestors were small and nocturnal. In daytime, the mighty dinosaurs ruled; our mammalian ancestors had to contend themselves with the night.

As a consequence of their nocturnal lifestyle, early mammals lost two of the four opsins which they had inherited from their para-reptilian ancestors; up to this day, almost all mammals are red-green colorblind, if they can perceive color at all. The poor color vision of mammals can be contrasted with the most excellent color vision of birds, which have retained the exquisite color discrimination of their dinosaurian ancestors.

Being mostly colorblind, mammals have never felt a need to develop colorful coats; the main evolutionary driver for spectacular colorful integuments is sexual selection, and sexual selection can only work on what the senses are able to sense. This is why mammals have such a reduced palette of colors, whereas the birds are resplendent in their fascinating colors.

Same star, same planet. Different evolutionary history.

   

^{Left: two avian dinosaurs, a Scarlet Macaw (Ara macao) and a Blue-and-gold Macaw (Ara ararauna). Photograph by Flickr user Eddy, available on Wikimedia under the Creative Commons Attribution-Share Alike 2.0 Generic license. Right: two mammals, mother chimpanzee with baby. Photograph by Böhringer Friedrich, available on Wikimedia under the Creative Commons Attribution-Share Alike 2.5 Generic license.}

Among the mammals, we the catarrhines (Old World monkeys and apes) are the only ones to have evolved trichromatic color vision. But that was not so long ago, only about 30 million years. Given enough time, and assuming that we don't make them extinct first, it is quite possible that in one or two or many lineages of Old World monkeys mutation and sexual selection will do their thing, and our distant descendants will get to see the emergence of colorful furry arboreal humanoids.

Answer 2

As far as I know those details does no affect skin color. The skin color is a mixture between the color of you alien's blood, their enviorment and their skin thickness. Iron is the molecule that transports oxigen in the blood, and is red when oxidized, this combined with the fact that our skin is translucent (absorbs and reflects light, which can be seen most when we cover a flashlight with out fingers) which will make the human skin always a derivant of a reddish tent- even when the skin tone is darker as a result of melanin. However, iron is not the only molecule- for example copper based blood would be blue and with translucent skin would give a blueish tone and there is also an illness that makes the blood green. Ofcourse skin is not always translucent- your species could have a thicker skin/hide to protect them from eviormental threats (dust storm and parasytes) to which would negate the blood as a main factor in the color. However your species might really on pigment coloration either for camouflage or mating giving you more freedom with what you want to do. Another example are poisonous species that unusally are very bright and colorful in order to warn predators of their toxicity.