Apple has given consumers an ultimatum.
Keep it or return it. Period.
They will allow ONE screen replacement.
If you don't like it, return it for a refund.
Apple is NOT going to fix this issue. These are defective monitors. They ALL have yellow blemishes in them. It is what it is. Apples specs allow this.
Know that if you order an iMac it will most likely have yellowing. You either live with it or return it. That is what Apple has essentially stated.
Buyer beware.
Honestly, I'm waiting on my SECOND screen replacement. The first one had severe backlight-bleeding. So, Appl asked me the get another LCD replacement. If it still has any problem, they will change the new one for me.