The Sony Xperia S is a very attractive phone -- I'm testing one right now -- but users overseas have complained that there may be defects that cause a yellow tinge to come across its otherwise gorgeous 342ppi display screen. Sony Australia's commented on the issue, which it says affects only a "small number" of units.
The full response to our question regarding the yellow tint issue is below. Of note, naturally enough, is the slight dig at direct importers; while Sony's technically correct, under Australian law the merchant that you purchased an Xperia S from (in this case, the direct importer, whoever they are) would be your port of call for screen issues.
Sony Mobile Communications has identified that the display on a limited number of Xperia S smartphones may show a slight yellow tint if exposed to temperatures above 40 degrees Celsius. This is limited to a small number of units and the cause of this has been corrected. Any consumer observing this slight yellow tint on the display of their Xperia S is welcome to contact their local customer service centre and Sony Mobile Communications will resolve this at no cost to the consumer.
Sony provides warranty support for products that have been sold in country by Sony which meet local regulatory compliance requirements. Products purchased overseas will need to be returned to the place of purchase or country of origin in order to redeem the product/stores warranty obligations.