think of it this way... your desktop is making it look "brighter" than it is. while FCP is attempting to simulate an accurate gamma that should "match" how it looks on a client monitor.
Well, I don't have a good HD monitor other than my cinema display, I'm wondering if I should invest in a second cinema display or a high quality HD monitor for that ( would a consumer plasma or LCD do?, I actually have a CRT 30" HDTV would something like this be accurate? )
From my understanding, FCP makes the footage look a little "darker" because it shows you what your footage should look like on a TV (where the gamma curve is different of that of a computer monitor). I have noticed that if you export footage to quicktime, the footage looks brighter and has less saturation (when viewing on a computer monitor), but if you then put that same quicktime file on a DVD or something and play it on a TV, it looks very similar to that from the FCP canvas screen. That is why it is crucial to have an external calibrated production monitor when color grading. So to sum up what I just said:
The footage that you see in FCP is "simulating" the look that should be represented on a TV....so to speak.