Quote Originally Posted by Bob Carnie
If you are printing colour negative there will be times that you will require to use cyan filter to achieve the colour balance you want.(cross process negatives come to mind) This will be in conjunction with either the yellow filter or magenta filter (but not both) using all three filters will only add neutral density.
Not quite. Depending on how much color correction is necessary, cyan may be added to increase the effect of yellow and magenta correction. I've done a bit of work where the model was illuminated with the light through a color transparency projected with a Hasselblad PCP 80 projector. The bulb in this puppy is rated at something like 3600 Kelvin, but after the light passes through the transparency, that is really no longer relevant. The film used is Agfa Optima 100 - balanced for daylight - 5500 Kelvin.

Printing is done with all three filters: yellow and magenta are not enough by themselves.