You use the track mattes(F4 to access) to create stencils. On the top layer, you mask the areas you want to show through, place a layer below that is to be used to accent, then change that layers track matte to "alpha matte".
You may have to duplicate & place the original video layer on the bottom. If you do that, you might want to play with the transfer modes of the "highlight" layer.
Check out this tutorial,
Keying and Transparency
Johnny Cuevas, Editor
Thinkck.com
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.