Part of color grading is re-lighting a scene. Unfortunately, Sony Vegas doesn’t have a 3D lighting system like After Effects has, but it’s still possible to hack together some basic re-lighting using Bump Map plugin’s “spotlight” template.
For some weird reason, stacking 3 Bump Map plugins in their own tracks (to emulate a 3-point lighting) is very sensitive to 8-bit processing, and they end up canceling each other out. However, it works lovely, and as it should, when using 32bit processing in Linear mode (mode is available only on Vegas Pro).
Here’s an example of how important grading, lighting, and 32bit processing is.
Picture by Melissa Ann Barrett, licensed under the Creative Commons “Attribution/Share-Alike” 2.0 license.
I hope that Vegas will eventually introduce proper lighting functionality, so this way the need for 32bit is minimized. Nevertheless, this article should show you the need for re-lighting while color-grading. Turn on/off the bump map plugins on the project file linked above to see how much re-lighting helps.