Thanks everyone for your replies. Jens, a very informative response.

http://www.talkgraphics.com/images/smilies/redface.gif Perhaps I should explain that my posts above were more of an attempt to pass along some very basic info in a humorous way. I've been told that my sense of humor can be very bizarre at times.

I used to teach advanced colour techniques, which included how the human eye's rods and cones respond to light. I also won some Air Force photography awards in the creative catagory for my use of isophoto mapping. A technique used most often to apply colours to astronomical images.