srs5694
Member
Cyan need not be touched unless you run out of magenta and/or yellow, or unless you want to dial in very precise amounts of neutral density. Cyan works opposite the other two filters, since it is cool and the other two are warm; another reason not to use it.
FWIW, on my enlarger, I require cyan filtration, along with increased magenta and yellow, because without that my printing times are too low, even with the lens stopped all the way down. I also like to start with some cyan because that makes printing a complete color ringaround a bit easier; I can subtract 5 or 10cc of cyan rather than add 5 or 10cc of both magenta and yellow.