It's possible that it is just the glue and that it will go away, give it a week or two (if you can) with regular use and see if you still notice it then, if you can then take it back/exchange it Hope this helps
No wonder it's called refurb. It was previously returned by users that bought it due to yellow tints. Apple service tech didn't do anything with it and called it "IT'S WITHIN SPEC". That's what you got.