Both are 5S'....
Most 5S' I've encountered are yellow... At this point, I really think perfect white display is the defect.
Yellow-ish bar at the top? According to a Genius, it is "within spec." It used to bother me because texts change color when scrolling up as they go through that yellow area... But now I live with it. I'm sure all other 5S' do it, so what can I do?
Imagine if a new Samsung phone had a non-uniform display. People will ditch it, and purchase other manufacturers' superior phones - Nexus, Xperia, etc. But Apple? We keep going back because iPhones are the only phones that offer iOS. Some people get stuck in "exchange lottery." Can you imagine doing that for a Samsung phone - exchanging your phone more than 3 times to get a perfect unit? No... You return it, and try a different phone from another manufacturer. Do you think I would have lived with a Galaxy with yellow-ish bar at the top of the screen? No! I would have gotten an Xperia. But I kept my 5S. Did I have any other choice? No. So don't you...
Also imagine if a Samsung phone rattled... Well, we probably would be saying different things instead of "it's design choice," or "it's normal."
But let's not forget iPhones are still technological marvels. Yes, they have flaws and imperfections that can affect user experience, but fact of the matter is that iPhones are top-of-the-class phones when it comes to features, performance, etc. Apple could have done a lot worse with this iOS monopoly. Remember MS in the 90s? At least Apple isn't like that, for now.