I've seen a number of posts regarding a gamma shift happening after exporting to QT from FCP. I'm now experiencing the same issue. However, what's odd is that after exporting 'current settings' (1920x1080, ProRes) the quicktime is washed out but, taking the exported clip back into FCP, it looks fine. Thing is, if I take that same export and put it into MPEG Streamclip, or VLC, it's still washed out. So why would every player give me a washed out image but in FCP it looks identical to what I'm seeing on the canvas? Quicktime was set to 'FCP colors', etc., so that's not a problem.
#1: What you see in the FCP Source and CANVAS are not color accurate. Not by a long shot. The only way to see a color accurate image is to view this on an external broadcast monitor, or good HDTV, via hardware IO devices from AJA, Blackmagic and Matrox.
#2: Quicktime isn't all that accurate either. Mainly because computer displays have a different color space than TVs and broadcast monitors.
#3: Various players will play video differently. WHY? No idea, I've noticed that too.
Main thing is that if you are editing videos that need to look good on the web, FCP 7 isn't the best option. FCX does better, as does Premiere. Because they know that a lot of people edit videos that are planned on being viewed on computers or the web, so they designed their interfaces to capitalize on that. FCP 7 was mainly a broadcast editing software, so was aimed at broadcast workflows and viewing options.
Go to System Settings/ Playback Control/ and change Gamma Correction from Accurate to Approximate. Now everything will look washed out in the timeline as well, same as in QT and probably VLC.
The only way I've found to correct this using Apple's software is to add Gamma Correction in Compressor. I remember reading that someone suggested 2.0 was the appropriate offset. I set mine at 1.15. It still isn't perfect but I do find it to be an improvement, at least for simple web videos. For anything really important, I'd be spending the money to have it fully colour corrected, even upon export.