Still kind of new to AF (using AF CC) and here's one I can't figure out. I've been through the manual and the You Tube tutorials, but no help. I have a color shot of a room that a man walks through. I want the room to remain in color, but the walking man to be black and white (sort of a ghost thing I guess). Other then many hours of rotoscoping, is there a simple way to do this? That's it. Thanks for any help!
Try using Rotobrush to separate the subject from the background. You won't have a single bit of luck with Rotobrush unless you read up on it and run tutorials. In AE Help, use the search term rotobrush and a boatload of useful information appears.
Got the subject all rotoed nicely? Make the subject B&W and put it over the original color shot.
The video linked to from the first item in the bulleted list here shows the basics of how to do this kind of thing with Roto Brush: