Return it and get a new one.
Not always necessary and
certainly not apparent with just a pair of shots from two different computers with a digital camera. For all we know the 'cool (white/blue) monitor could be 'off' while the 'warm' (yellow) is closer to 6500°
Warmer is traditionally easier on the eyes as well as easier to set up print profiles (again....assuming the display IS within spec and not too outta whack!)
FWIW---I've got a 2012 pair of rMBPs. One came stock with an LG. The other a Samsung (wife's). Out of the box...the LG 'looked' closer to white but within a couple of months the IR creeped in and got significantly worse. Had the panel replaced and it was almost identical to my wife's Sammy, my iPad 4 and iPhone 5. We were having a new front projector installed in out HT room and while he was calibrating the projector I asked him to check out the rMBP displays. They measured @ 6438° on my wife's. 6510° on mine. Damn near dead on. For S's and Grins...we checked our older, cooler 17" 2011 models. One was at 7000°. The other nearly 7100°. And these looked 'right' to me! After a year's usage of the rMBPs I've noticed I strongly prefer the warmer (lower---closer to 6500°) displays much more to the cool, higher temp panels
Extremely hard to tell with a CMOS digital photo. As it'll try to find the correct white point itself and accept that as 'true' white, meanwhile showing yellow (or blue) pending whatever display wasn't selected either automatically by the camera OR the user shot the whiter/bluer screen as the correct white point to the cam. Hard to say. But again...don't be so quick to return it. If you can take it to the Apple store and do a quick side by side with a couple of their on shelf displays. From there you should have an idea of where your panel 'sits' within Apple's specs
These calibrators, how do they work?
.....
And one last question.

Can you recommend some cheap calibrator that is not hard to use.
I don't need super perfection, since i don't do professional work. But a good calibrated screen would be nice.
I've always wanted one to calibrate my TV's and computer screens. But I don't want to spend a lot of cash on it.
Do you have a local display calibrator in your area? One that knows what they're doing? It was my experience with my original 'flat panel' LCD and my of RPTV that post calibration..it didn't look 'right' to me...but after a couple weeks watching BluRay flicks to standard HD cable; skin tones were more real, the natural colors were evident immediately...and once used to a 6500° display...it's an enjoyable experience. That said, you get what you pay for. There are $69 calibration kits and $2800 units and software. Only so much you can do without experience and going 'cheap'
We use Eizo and NEC displays for color correction video and print finalizing and printing for sometimes pretty large prints. I find my 2012 rMBP pretty damn close to the higher end panels used for final output
I've spent hours calibrating mine. The yellow is just inherent in the Samsung screen. If the yellow tint is rather moderate like mine, live a blissful life and pretend it doesn't exist.
If it's extreme, then go on and make a Genius appointment.
Or we've become used to blue/white and high brightness displays over the years, and your display on your rMBP MIGHT just actually be accurate in comparison to your older displays you've become accustomed to.
Mine is regular for the top 3/4's of my screen, but the bottom half has a slight yellowish tint. Its annoying as hell, plus my keyboard and trackpad locks up when it feels like it. 1st Mac....
Not just the color shift....but an unresponsive keyboard and trackpad are deeper symptoms than a bad display. You're well under warranty. Take it back. They'll gladly change you out. Apple's post purchase support is A#1. Make sure you're happy. These aren't small investments.
If the display is not uniform, it's defective. Partial yellow or purple tint are common manufacturing defects in IPS panels.
If you are within the 14-day return period, send it back.
Or within the first year (& without AppleCare). Doesn't have to be 14 days. They change the panel out and any defective parts. You may be a candidate, regardless of purchased date for a total replacement...pending repair time and parts.
If his monitor is yellow tinted, then any yellow in the image will be even more pronounced..
Without knowing the white points of the displays, or the camera, you have no way of saying which one is neutral.
Precisely. CMOS sensors are notorious for showing us what is or isn't white. Unless you white balanced your camera before you took that pic...chances are we aren't seeing an accurate depiction of the actual colors you're seeing. It's definitely obvious one is warmer than the other but don't dismiss the 'yellow' display as bad. Measure your white/blue panel's color temp to see they haven't calibrated that one to 7200° or some over the top, non standard white point
You don't need to return your rMBP, your computer still thinks you have a LG panel, do this:
1) Go to the path "Library/ColorSync/Profiles/Displays" and delete the old default profile, look for a file named like this "Color LCD-00000610-0000-A00E-0000-000004280380.icc", if you find more than one delete them all.
2) Restart your machine so that MacOSX can recreate this file for the Samsung default Color profile, the yellowish color should have disappeared.
3) Calibrate to your taste.
Did he have his panel replaced? If it's stock, it KNOWS the color profile and calibration was done with Samsung. Not LG. Why would it 'think' it's still calibrated as an LG when it shipped with Samsung? I'm not following you here
IMO....as far as the 2012s are concerned, Samsung, with internal and external battles on patents aside....are providing Apple with some extraordinary IPS panels. Samsung makes a sh-- gob o' cash from Apple. It still (in business) behooves them to supply top notch displays (as they aren't using this resolution of panels on their lineup---they're being designed and built specifically for Apple). I don't buy the fact they're passing down second rate/tier displays to their biggest client buying these new IPS panels that are probably pretty lucrative to Samsung and are generally considered a better display than LG
Good luck OP. I'd spend some time really using your 'yellow' Samsung. Do some printing of photos. Manipulate some simple video from your iPhone, GoPro or DSLR....and play with it. If you have a broadcast display around your house, play the finished product through your everyday LCD/LED/Plasma TV. Tell us what it 'looks' like once you're done
J