Various colour enlarging techniques with different materials and processes over the years have used Cyan filtration, however with RA4 you shouldn’t ever require Cyan, unless as described by Bob D569.

That said, Cyan is actually controlled in colour negative printing by density. If you have a print that is too dark, then you will mostly find it is a bit red, usually one or two units too much.

By pulling the exposure by around ¼ of a stop in time, or by changing the aperture by about a ¼ of a stop to reduce the exposure, you will accomplish two things. You will have made the print lighter, and the red should disappear. Effectively adding Cyan!

Mick.