This could potentially be a subjective issue. The first thing you should try to do is compare screens of yours and another M8 to see if there's a difference. You can't compare it to other models because every model will have some color differences. If yours is the same as another M8, then it's likely not a defect, but just how it's designed. At that point, you either have to live with it, get a different phone, or perhaps try a screen filtering app. I've seen some filter apps that can overlay differing colors to tint the screen. Not sure if something like that would work for you or not.
If your phone is different than another M8, then I'm guessing a defect. There's no way that I know of to adjust the colors by default like you could with a tv. I'd try a warranty claim in this case if you're still in the warranty period.