Chandan Kumar with a tutorial on using RGB passes out of a 3D application inside of After Effects and using them for flexible compositing. In this tutorial, he is using MAya for the 3D application, however RGB passes can be made either automated or manually anywhere really.

“In this tutorial we will learn about “RGB Pass Compositing” in After Effects. RGB pass compositing is something that gives freedom to the compositor to work on individual objects rendered from 3d applications. It is a well known and much used technique in production houses. This tutorial covers both the rendering technique from Maya and the compositing method within AE.”