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If you press the MENU button on the TV, does the Samsung menu look OK or does it look like it might be missing red, too?
OK, just let me know!
I'm going to take a wild guess that you are watching a high definition set top box, either cable or satellite, and it's connected to your set via the 5 wire component video connection, correct?
If so, what you have is a loose or defective red video cable. Try wiggling it on both ends and see if that doesn't fix it. If you had a problem with the green cable, by the way, you would get no picture at all.
Let me know if that works, and thanks for using JustAnswer!