I'm going to bump this.
Bought a silver Xs on Saturday, I ended up returning it. Under the right light I noticed it had two spots on the back glass that looked like water/chemical etching, and they would not come off at all. Also, noticed a yellow halo/tinge around the entire screen on a bright white page that I initially didn't see. Returned.
Device two has a better screen and initially seemed perfect, but under that same bright light I noticed a spot that looked like chemical residue and another spot that was clearly a chemical run on the glass back. Again, wouldn't come off, seems it may be under the glass? Haven't decided if I'm going to keep it (perfect otherwise and yes, it is hard to see the drips in the glass unless you're looking for it in the right light), but this is also a purchase I don't need to make and if Apple is going to ask a grand, I feel justified expecting something without obvious flaws.
Undecided. Keep it, exchange it once more (that would be the last try), or just return and go back to my 8.