Replace it for new one
Everyone should replace iMac if it has yellow tint issue - and yes its annoying doing photoshop work or even surfing the internet.
I had significant issues with my iMac, particularly given my issues got worse after the 14 day return policy.
Initially in Hong Kong Apple offered the repair route - I was most annoyed given I'd one iMac already in for screen replacement and this new 27in i5 3.1 was to be its work replacement.
After a couple more attempts in Asia, I was transferred to customer relations in Ireland and the issue was remedied after 30 mins on the phone with Apple being most apologetic about the matter.
To sum up, the iMac should perform flawlessly at least within the first 4 weeks - if it does not, Apple should replace them - after a month, I accept that repairs may be the route to go.
However, given I'm getting a replacement for 27in i5 3.1, I've decided to upgrade to a BTO option and move to i7 3.4 processor and 2G of VRAM.
I have no need for SSD, but would like to increase HDD size - I can hopefully do this a little later by going to a 3T WD - our local repair centre will replace for around US$25.00 - I also get to keep original drive which can be utilised as a time machine - just waiting for 3T prices to drop a little more.
Even with all the nonsense, once you have a fully functioning iMac they are great machines, especially the latest 27in for DTP - a Mac Pro is overkill now for the work I actually undertake.
Also hoping to move from 12G of RAM to 16G once I have a few spare pennies - can I use the 2011 DDR3 1333 in the late 2009 iMac - any yes I know its 1066, but hoping it will accept 1333 RAM, bring me up to 8G in my one iMac 21.5.