Ok, compared to my co-workers iPhone 4S his has a blue hue while mine has a slightly yellow hue (seems to be getting better?). I checked where mine was made and here's what I dug up.
Using this site I was able to check where my iPhone 4S was made
http://www.chipmunk.nl/klantenservice/applemodel.html:
My iPhone 4S
Serial number: C38xxxxxxxxx
Name: iPhone 4S
Model: iphone_4S
Group1: iPhone
Group2:
Generation: 6
ModelCode: iphone_4S
Machine Model: iPhone4,1
Model introduced: 2011
Production year: 2011
Production week: 41 (October)
introduced test: GOED
Family name: Become a pro user to see this information. (sorry)
Screen size: 3.5 inch
Screen resolution: 960x640 pixels
Colour: Black
Capacity: 32GB
Factory: C3 (China)
Buddies iPhone 4S
Serial number: DNPxxxxxxxxx
Name: iPhone 4S
Model: iphone_4S
Group1: iPhone
Group2:
Generation: 6
ModelCode: iphone_4S
Machine Model: iPhone4,1
Model introduced: 2011
Production year: 2011
Production week: 40 (October)
introduced test: GOED
Family name: Become a pro user to see this information. (sorry)
Screen size: 3.5 inch
Screen resolution: 960x640 pixels
Colour: Black
Capacity: 16GB
Factory: DN (China, Chengdu - Foxconn)
The main differences are in bold above, I'm thinking the different factory is the cause here but again I could be wrong.