Panasonic TH42PX70 Purple Snake/ Magenta Noise
If you've frequent any of the more popular home theatre forums, you would have stumbled across lots of complaints from Panasonic plasma owners about a problem that is technically known as magenta noise, but is called as "purple snakes", "purple ants" or "magenta bands" on forums.
These usually occur on areas of the screen displaying a very subtle and light gradation (typically biege/ cream). Purple/ magenta fizziness amounting to serpent-like bands would pop up where they shouldn't, hence the term "purple snakes". Some well-known movie scenes which will test even the best plasmas to bring out this phenomenon are the underwater scene in "Harry Potter and the Goblet of Fire" and any scene depicting a pale wall in "Flight Plan".
Apparently these magenta noise occur due to the inability of the processor on Panasonic plasma to correct handle and render such subtle gradation to the extent that the processor had to overcompensate and "push through" magenta colour. To Panasonic's credit, they have been going around fixing new D-boards for owners who suffer from the worst bands, but so far the feedback is that the solution is still hit-and-miss.
Before you worry too much about your Panasonic TH42PX70, professional tests have shown that they too exhibit purple snakes, but so significantly less that sitting from 6 to 8 feet away you won't be able to notice it. If it remains a problem you can contact Panasonic through your retailer to see if they can swap the plasma for you.