I'm so glad I found this thread. I had yellow tint issues with my iPhone 4S, which meant colours weren't rich and appeared wishy-washy, much like you described, goosel.
I was therefore delighted when I pre-ordered and recieved my black iPhone 5 32GB on release day and the screen was rich in colour, really crisp text with deep colours (looks very much like the colour tones on icon707's iPhone 4 picture a few posts above. My black iPhone 5 has a similar colour temperature and sharpness to my Retina Mac Pro.
I was considering changing to the white iPhone 5 and either selling my black one or keeping it as a spare handset for a family member etc, so I went to the Apple Store in Southampton (UK) yesterday where I had reserved a iPhone 5 white 32GB (took 8 reservations to get hold of one). After turning it on when I got home a couple of hours later, I was dismayed to see the screen had a yellowish tint, the colours weren't rich and the text was slightly hazy (all of this was particularly noticeable when you put the two iPhone's side by side). I took it back to the Apple Store two hours later and showed them the difference (a good example was putting them side by side in the messages app, or in brightness settings page). They declared it a DOA and replaced it immeadiately, but the same yellowly screen was present on the brand-new replacement (not a warranty replacement, a return and new purchase). The third new iPhone yesterday was the same, at which point when they offered to replace it once more but I refused and took a refund instead as I had had enough by that point.
However, this isn't an iPhone 5 issue across all the 5's produced because the display models in store were the same crisp screen as my black one is on both their black and white display models. Colours were rich and text was crisp on almost all models.
When comparing my crisp screen on my black phone to the yellowly screens on the white ones i was sold yesterday, it does look to the yellowy screen that it has a slight bluey colour temperature but it makes things more vibrant and look great.
The employees (the store manager and a separate iPhone specialist) agreed that there were large differences in the screens, and were very apologetic saying they had never come across such differences before and they would report it back (their 'surprise' at the issue is, I expect, because if I hadn't had a 'good' iPhone 5 screen I wouldn't have noticed the abnormalitily of the yellowly poor colouring on the ones they sold me and I returned yesterday).
I really want a white iPhone 5 with the screen I have on my black iPhone 5, but it seems pot luck due to the (perhaps) different screen suppliers they use?
Really dissapointed in Apple's Quality Control on this. I love the iPhone 5 white, but won't take it unless the screen is the standard I believe it should be, as evidenced on display models and my black iPhone 5 device.