The color of the Martian sky depends heavily on how much dust is in the air, but it's generally orange-ish, while a dust-free sky would probably be black! People have scienced the hell out of this. For example see: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200...
The question of what it would look like to human observers is another matter. A lot of photos from Mars are color adjusted to try to capture what we'd see if we went in person.
The question of what it would look like to human observers is another matter. A lot of photos from Mars are color adjusted to try to capture what we'd see if we went in person.