There is a new firmware update for the PN50A550 which is the US version of the PS50A550 / PS50A556.
It’s being discussed here on AVforums:
Robert: On your website there is a new firmware listed for my pn50a550. What problems does this firmware correct?
Dylan D: I will let you know about it.
Dylan D: Let me check that for you.
Robert: ok thanks
Dylan D: Firmware update will fix intermittent red blur when watching moving pictures. It will enhance the color processing capabilities of the TV. It will fix a problem with a totally green screen when connect to certain HDMI devices. It will improve the WiseLink detection.
Dylan D: Is there anything else I can help you with Robert?
Robert: Is that all the update addresses?
Dylan D: Yes Robert. I am reading directly from the service bulletin matched to this update. Have I answered your question?
Robert: Yes, thank you.
I do hope that this update will come soon to Europe also, as the european version is still flawed with false contouring. Actually I believe both versions are flawed, guess you only notice it on PAL source material.