Have you actually tried viewing a test card, to see whether your screen is set up correctly? If you're using Freeview, here's how to do it:
http://www.ukfree.tv/helpme.php?faqid=1107051204
The column of boxes to the left of the central picture should be bright white at the top and jet black at the bottom, but with the boxes in between clearly showing intermediate steps. (i.e. the second box mustn't be so bright that it blends into the white one and the second-from-bottom mustn't be so dark that it blends into the black one). Further, the colours across the top mustn't be too bright (closer to 'pastel' on the left particularly) and the girl's skin tone should look untanned and natural.
The vast majority of TV sets in people's homes aren't set up correctly, so it's unsurprising when they report problems with brightness, contrast or colour balance.