I think it's important to note that in most "normal" cases .. color corection is done to fix footage from a camera that is not properly balnced for the light conditions where it is shooting. Most of the time most of the colors are there but in different proportions than for what the camera is set to.

Underwater shots are different in that various colors are subtracted the deeper you go. If the color just isn't there in the first place I don't think you can "correct" the scene to put it back in.

Of course the loss of color is gradual and it all depends on the time of day, the intensity of the sun and how deep you shoot.

Maybe investing in an underwater video light might be a good (but expensive) idea.

I was hoping someone would post a nice write-up for you, since I would like to read more about it, as well. The "Color Corrector," in particular, provides a great deal of control. It seems to me that the "Color Curves" plug-in is mainly used in a trial-and-error manner, at least in anything but maybe Vegas Pro (since Vegas Pro has the vectorscope tool that Vegas Platinum Pro doesn't have).

I can offer a few tips that perhaps you haven't already discovered on your own, though.

You could grab a frame that has good colors and exposure and contrast and brightness that you want to use as a reference to match other footage against, and then display that captured frame in another window, such as with Windows Picture and Fax Viewer. You might find it helpful to have a reference available for side-by-side comparison purposes as you work on other clips to achieve an overall consistency.

If the correction a clip requires varies as that clip plays, such as when you pan your camcorder, you can use the keyframe editor at the bottom of the plug-in window to "animate" the corrections you apply, i.e., to apply time-varying corrections.

You can Google words like gamma to find online descriptions of them in greater detail than Sony provides in its help files. The theory of gamma, for instance, isn't specific to Sony Vegas Platinum Pro.

If you want to correct the hue of a clip, such as one that has an overall bluish tint, without just randomly adjusting parameters then in the "Color Corrector" plug-in, you can find some area within the displayed image that should be neutral in color (black, white, or grey) and use one of the "minus" eyedroppers that corresponds to black, white, or grey (mid tones). Click the eyedropper on that portion of the image and it will subtract the hue that was cast over the neutral color from the entire image. In other words, the minus eyedropper for black, for example, clicked on a portion of an image that should be black but isn't, will make it black and adjust the entire image accordingly (effective assuming the same hue had been cast over the entire image).

I have never used the vectorscope that comes with Vegas Pro but not Vegas Platinum Pro (because I have Platinum Pro), but without that I suspect you may have to rely on trial-and-error, and your intuition as you gain experience, for knowing what types of adjustments you ought to apply first. I imagine the vectorscope is intended to help guide you in your adjustments with less of a trial-and-error approach.

I suspect that once you find some corrections that work well, that you should try to use the same types of corrections to all your clips that require correcting, so that you will tend to have a consistent "feel" to all your corrected clips. It also saves you a lot of time if you can apply the same steps to each clip to correct it, rather than having to reinvent the wheel on each clip you correct.

If you have one of the nicer photo editing programs, you might spend some time studying its color correction capabilities. Since photo editors are much more focused on correcting images than video editors are, you might find better explanations for how the tools work. Of course, the photo editor will not work exactly the same as Sony Vegas color corrector plug-ins do, but gamma is gamma, and contrast is contrast. You might gain more general insights from a program that is more focused on color correction specifically that you can then apply within Vegas.

There's a lot that can be done with the color correction tools, and a lot of people could make their videos more interesting or have greater impact if they used the color correction tools more than many people do.

Hopefully, something I've written will be helpful to you.

A hint from a professional color corrector who has worked with thousands of underwater stills:

Rule #1: Correct for the whites on subjects that are close to the camera at mid-depth. (You didn't say whether you were using all natural or artificial light, but the principle is the same).
Rule #2: Leave the rest alone.

Rule #3: When in doubt, refer to rule #2.

Water filters yellows and reds from the gamut. You can't put it back in. The result is a blue / cyan cast, which is more pronounced the farther you are from your subject, and / or the deeper you are. You'll have to live with it, unless you have strong artificial lighting and you are very close to your subjects.

Our fellow user, Nick Hope, makes his living doing this. He may be able to shed a little more "light" on the subject.

As for learning color correcting, it is a science / art combination that takes years to learn. Don't even think about gamma and curves until you have mastered the six-point basics. Plenty of free resources on the internet and links to tutorials by your fellow Vegas enthusiasts available (Ed Troxel aka jetdv comes to mind) by doing a search.