Interesting topic Gamma.
http://www.photoscientia.co.uk/Gamma.htm

While the above page is mainly aimed at computer monitors, it applies to TV's as well, in fact all video media. Excuse me if I ramble a bit. The gamma settings in the PC world are slightly different than in the Mac world. That means if you spend a lot of time doing graphics on one platform then give the work to someone viewing them on the other platform they either will be too dark or washed out. So too if you attempt to do color "corrections" off a computer montior for videos that will be viewed of a TV.

New in version 4 you also have GAIN, which works like Gamma. Plus you have scopes which can show a histogram and the luminance waveform

Confused yet? I did write a few tutorial that go into more detail.

http://www.wideopenwest.com/%7Ewvg/tutorial-menu.htm

The point of all this rambing on is rather simple. Actually three main points.

1. If you are working on videos that are to be viewed off a TV, then you should be making adjustment off an external monitor. The above web page gives a rough idea why.

2. For best results use the following filters:

a. Color curves (generally first)
b. Levels (version 3) or Color Corrector (version 4) *see below #3
c. Do NOT attempt any correction of hue until you have the luminance right.
d. The controls in the levels filter and Color corrector effect all pixels more or less the same amount.
e. Color curves effect HOW the pixels are distributed, which you can control by building a curve. Which is generally the best method, since you have far greater control over what's happening. I know I rant on this a lot. <wink> Because I can take a really crappy image and turn it into a masterpiece. Well almost.

3. OK, you got a fairly decent looking image. You may have adjusted the gamma and/or the gain and offest a bit to balance the histogram and fine tune what you did with color curves. Now tweak gain and or gamma a little and you'll find you can often increase or decrease saturation. Which you'll do if any depends on your source file. Rarely will you get the best results leaving saturation gamma and gain at their default settings.