J-O Eriksson led the way on quickly modifying a Community Server color scheme in his now classic "Create a New CS Skin in 5 Minutes." This nuglet is a variation on J-O's theme. "J-O's Theme." Ha-ha! I crack myself up.
Using the incredible Firefox Web Developer Add-On, we can quickly view colors used on a page. We'll look at the Forums page.
We can eyeball the color we want to change, Ctrl-Shift-H in Visual Studio and have at it! A couple sidebars on this are 1) we'll want to be careful changing neutral colors like #CCCCCC en masse, and 2) In CS2007 we'll want to be sure to include any color settings in the DynamicStyle.aspx and theme.config files.