Donald, if you use c and y together and add numbers you can reduce m. if you use c and m together and add numbers you can reduce y. maybe something like that is going on here. but glbeas is correct that cyan is the subtractive of red and yellow is the subtractive of blue and magenta is the subtractive of green. Are the colors wheels marked on the enlarger head? I would think that they should be. Just a thought.