Both blue and green screen are called chromakey. Chromakey green generally has an advantage over blue. More people wear blue than green in their costumes, making it the choice of most chromakey users. Of course, if their is green and blue in the scene (besides the screen) this won't work. There isn't actually any rear screen projection involved. The blue (or green) is electronically replaced by source video from a pre-recorded videotape, videodisc, camera, etc... and is primarily used in situations where it is either more cost effective to use stock footage, or would otherwise be safer than performing dangerous stunts which may be created with a combination of animation, models, and movie magic. Ron Hebert, Executive Director Broadcast Training Institute ---- Screen-L is sponsored by the Telecommunication & Film Dept., the University of Alabama.