I just had my tube changed on my JVC 36" HDTV an hour ago. I have had purity problems ever since i got it 6 months ago. It looks alot better this time but i still dont believe it is pefect. I do have a purity setting in the menu but i can't seem to find a good color screen to set it with. Is there a way to get a plane white screen on my tv so i can look for light blueish corners??