My 7+ is also warmer then my 6+ but I do not believe this is because of a defective display. It's calibrated this way for accuracy. It is also notably brighter then my 6+. Warmer colors are also easier on the eyes.
Notice how the two 7's match and the 6 on the left is more blue. It is the nature of the display and not a defect.
I've been trying to tell myself that the iPhone 7 is suppose to be calibrated that way. But it bothers me when I've been going through photos and editing my iPhone images and the colours aren't coming out the way its suppose to be especially when my eyes are use to the iPhone 6 "cooler" display. I can use my phone all day and get use to the warm tone but when I start editing my photos for Instagram it just feels way too warm for my eyes.