"Like many others, I'd pretty much given up on this purple/pink banding problem, and just resigned myself to tolerate it until it reached a point I couldn't take it or when a good replacement option appeared. This problems seemed slowly worse, and I researched it one last time and found this forum. After following the instructions, using the normal remote and the "Hotel" option, I performed the update and the issue is resolved! It's amazing what a few lines of code can do! Thanks to everyone who helped provide this solution!!"
Add me as a happy camper as well with my 'new' PN58C550 that I got for FREE off of our local craiglist. Its previous owner's sons had bought their father a new smart replacement set so the father posted the ad for his old set and I was the first to spot it. As I was loading it into my car he said that he didn't think it was ready for the county dump. Boy was he right!
I haven't done the voltage adjustment. The pink/purple posterization with white backgrounds is appears to be gone and the TSB says only do this if the problem persists.