Just to broaden the knowledge of the technology for our small net.community I'd like to put a few words out on this imaging technique. Chroma Key is just one method. Ultimatte (TM) is another. Both rely on electronic compositing and not film printing. Black matte is preferred for lab compositing (such as for animtion layering). In both Chroma Key and Ultimatte the colour itself is arbitrary. As has been mentioned the use of green is costume and effects related and in the case of blue it is skin tone related. Ultimatte offers a higher level of subtlety to the effect in which smoke and shadows are not lost in the background. Although more difficult to manipulate, Ultimatte effects are more invisible and were designed from the ground up to be used for film resolutions. It is in the edges where one detects a "matte" or "key" in addition to the distortions of perspective for each layer. Some of my personal favourites are in the movies "True Lies" and "The Last Action Hero" but not because of the Arnold factor. In the video world of effects the colour blue is favoured because the effect usually features the faces of actors and for close ups. Check any "driving" scene in a daytime drama. There is little or no blue in the skin of white actors and the costume department can be careful what it offers for the effect scenes. In Film the effects are usually "larger" and require many layers of matte. Green is chosen for its increased contrast range and its purity of colour saturation without "noise". When adding electronic layers, contrast is the first (and most difficult parameter) concern. I've successfully matted with Red in the studio, but outside shoots are best with Blue because of the predominant colour from sunlight being in that range of the colour temperature spectrum. I've already begun to descend into jargon, so I'll leave it here. Dave Trautman Multimedia Specialist for ATL University of Alberta Edmonton, Alberta, Canada ---- Online resources for film/TV studies may be found at ScreenSite http://www.sa.ua.edu/screensite