But a quick google finds this to be something a lot of plasmas can exhibit. The fixes are all over the map but calls for service, if you are lucky mean a quick tuneup of internal non-user-serviceable adjustments.
At least it's not unique. If it was, that usually means the end of the set.
Bob
A pinkish discoloration appears horizontally near the top of the screen when the background display is a pale color (ie. snow or sky) but is not noticeable with a darker display. The discoloration is beginning to spread down the screen as time goes by. Is this a unique problem? Are there troubleshooting steps or recommendations you can supply? Thanks.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic