Hi All
Apple uses two vendors for screens and have for years. One screen is a crisp, clear, beautiful display that has the ability to be 25% brighter than the past gen. The other screen has a yellow or green tint to it, overall, that will never change (not glue) and will always be less sharp, less clear, and less bright.
If you are comparing one of the inferior screens to one of the good screens on a phone from last year, the phone from last year will appear brighter. If you compare a yellow screen this year to a yellow screen from last year, it will look the same. We do have some reports of people with iPhone 7s getting the good vendors displays, and those are in fact 25% brighter then last years good panels.
So the bottom line is - if your display is "warm" color wise, and is not as bright as last years phone, you need to exchange the phone until you get one of the good panels, which are the screens Apple promised in the keynote.