Why is a slight yellow tint a defect? Maybe it's just different than your 2010 MBP? Maybe your older MBP is too blue? Who really knows without an accurate frame of reference? I know my cMBP, rMBP, iPad, and iMac all have slightly different tints. That doesn't mean that any of them are necessarily broken, it just means there's display variance.
Type A: There are the yellow rMBPs.
Type B: And then there are all other devices in the Apple Store, and if you happen to have a Microsoft store nearby, all of those as well.
This is not a debatable slight tint. I tried (and failed) to correct using the built-in advanced calibration settings, the best I got (without fixing the uneven brightness and color shifts) was about a 800 Kelvin increase (= towards blue) to get rid of the yellow elements of the tint (it's not pure yellow, which why some on the forum have referred to it as pink, perhaps on displays with even more extreme variation).
Interestingly, all 3 LG screens I looked at today were shifted in the same (wrong) direction. Almost as if somebody had been using the same defective screen as a reference.
Since 2 LG rMBPs were in store, I assume those were from an earlier batch, while the 2.7Ghz rMBP I bought today was just delivered today (still on Lion, not ML, for what that is worth).
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Anecdotal evidence already suggests that there's enough variance between rMBP displays that calibration will be required in order to use these machines for any serious photo work. If you're saying that they essentially can't be calibrated because you might run into banding, then I think everyone is expecting way too much from these displays, because it's almost a given that you're not going to get one that's perfect OOTB.
I'm not a photographer but, despite your post,
this article suggests the the rMBP display responds very well to color calibration. I'd rather buy or borrow a calibration tool and get my current display as close to "perfect" as possible -- and risk banding -- than go through the trouble and crapshoot of the exchange game.
I guarantee you'll find it hard to convince anyone that a calibrated monitor isn't superior/more accurate for photo work (or just general use) than a fresh, non-calibrated, out-of-the-box display.
You have a good point, calibration (on a 8 bit display) is a tradeoff between hitting certain measurement points more accurately and having smooth gradients.
2 important factors:
1. the less calibration you have to do (delta E between actual and target), the less the impact on banding will be.
2. the less calibration you have to do, the more accurate the results will be. If variance is too great, you have a finite amount of calibration points and it is common to see at dE>3 that you cannot improve one point on the curve without making another one worse to an equal or greater degree. Classic interpolation problem.
Takeaway: With the limits of laptop displays being what they are, starting closer to where you need to be on display color accuracy is highly desirable.
Spending >$4k on a laptop that ships with a strong color cast, that is likely to get worse over time, is not a good move?