Desaturate all colors except (???)
 

In Vegas 7 in the Color Corrector (Secondary) how does one isolate one color and desaturate the rest? You can drop and drag the effect for red, but I'm sure there is an easy way to do the same for other colors.

Thanks.

This tutorial will teach you how to do it.
Edward Troxel has a tutorial on multiple color passes in his newsletters as well.

Excellent, thanks.

Vol 2 #10 of the newsletters has this article. First paragraph talks about passing a single color. Rest of the article deals with passing multiple colors.