The tinting varies from phone to phone, others are really that obvious while some are acceptable but still its a defect and a defect should not be acceptable regardless.
There are no special requirements as initially believed to see this issue, 0-100% brightness this issue is visible, does not require gray colors infact they are very visible in whites and when playing HD movies/animated films.
They reason why a grey screen is used to check is because the ease of just dropping down the notification bar or popping up the virtual keyboard, the issue is more prominent as the screen brightness lowers and dont think that 0% screen brightness is an artificial scenario unless you never use your cellphone in dark places or at night.
A defect is a defect regardless if a good majority of units are affected, But there are really good screens out there. We should not be complacent about this issue, the SGS1 never had this issue so why should the SGS2 have this and be acceptable right?
Reason why Samsung has not yet given an official word on this issue is that people are accepting this as normal, but with enough returns this is gonna turn some heads.
This issue has high possibility of getting worse as time goes by if its an actual screen defect.
It may not be noticeable for you now, but at the back of your head do you really accept a flagship device (@ $650)that is brand new with a defect?
A video example of the issue:
http://www.youtube.com/watch?v=hCfxCdtgxVw
Other screen defects include
1.) Ren tinting (rare)
2.) Visible suction cup marks on the screen, seen as back rings on grey/white images
3.) Too much oleophobic coating makes color shifting at angles very irritating
4.) small white spots on the screen, can be very visible with grey colors and other lighter colors ( common issue )