It's not glue, and it doesn't go away. It has nothing to do with conserving energy. It is panel manufacturing variability. End of story.
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Some are more yellow than others. Some have blotches of yellow, particularly on the left side. They won't go away.
It's not limited to iphones. It's on TVs, and laptop screens. Compared macbook pro screens in store, and some have yellow blotches on the left side, and some are all white.
There is a lot of misinformation out there about "warmer" profiles, glue, etc. I ordered something like 4 iphones back in September/Oct when they came out, and all came with horrible yellow tints. The Apple employees even thought nightshift was on, it was that bad. I waited for a few months, and recently, most of my phones have come with nice white and blueish screens. Only 1 came with one with a yellow tint on the left side. That's why I know it has nothing to do with the "warmer" profile. They wouldn't only give half the screen a warmer profile. To test the glue theory, I waited a week with each phone, and they were the same at the beginning and end of the week.
Only solution: if it bothers you, replace it. It's a lottery.