I got in contact with Apple online and they stated they had NEVER had any complaint avout yellow tint issues on any of their products and I was the first to address this kind of issue...
The 27" LCD panels the iMac use have had yellow tint issues since the first one rolled off the assembly line almost a decade ago based on reports from users. Every time Apple updates the iMac (2009 / 2011 / 2012 / 2013 / 2015 / 2017) the forum will soon have a thread with people noting it. People also reported it with the 27" Cinema and Thunderbolt Displays.
If LG hasn't been able to fix it in a decade, I assume they never will. I've been fortunate that none of mine have been noticeable unless I go out off my way to look for it by putting my display into a background color and brightness level I would never use (it seems to usually be in the lower right-hand corner) so I've never bothered to have Apple try and fix it because I was worried I'd end up with something worse. And nobody I have sold my iMacs on to has come back to complain about it, so I can only assume they don't notice it, either.