So I have created a scifi humanoud race with totally black eyes. There is no visible pupil or 'whites', it is just all black. The real reason is that I like the look as iy distinguishes them from other races who have more normal human eyes. Problem is that I cannot think of any way such eyes would offer an advantage.... despite research. Research reveals this: Eye color seems to have minimal but slight effect on color vision. Lighter eyes see colors more vividly but don't like bright sun, whereas darker eyes can track motion easier and take more sun. Animal vision traits seems like an option, even though their eyes don't look solid black (except some insects). Hmmm... wow. Guess I just answered my own question view thinking out loud. I can just make their eyes more sensitive to motion and be more resistant to eye damage from brightness compared to human eyes. To keep up their reaction times must be faster too, so they likely will have a faster metabolism than humans, prompting them to both eat and poop and rest more frequently than humans do. If you have any alternative ideas feel free to share them. I am also thinking to make their world have a slower rotation so they have longer daylight periods, giving good reason for having eyes that can deal witj brightness longer.