the protective plastic may 'trap' some air, or refract the color itself. When i bought my n6600 like eterneties ago, i had the same problem too. however, upon reading the manual, it said that it'd be okay after a few days, and if not, just send it back to nokia care centre. They'll either give you a brand new set or help you to repair it. Mine was ok afater a few days, and didn't really give me much problems.
btw..the problem is called 'dead pixels' if i'm not mistaken. =)