Hmmm. On my color enlarger the filtration is Magenta, Cyan and Yellow. I know that from what the manufacturers state the colors to which the variable contrast black and white papers are sensitive are blue and green. I know that my 4550 VCCE uses magenta and another color that doesn't really appear (to my eye anyway) as yellow. Perhaps I am color blind. It must be yellow though from what you say. Thanks for the information.