a) do you have any problem with your colour paper when printing? If not, it's dark enough.
b) do a proper darkness test, i.e. preflash some paper to midtone, progressively add coins every few minutes and process it. If you see the coin shadows, it's not dark enough.
c) if you can make out any forms in the room, e.g. your hands, it's not dark enough. Seeing a couple of pinpoint light sources after 30s of adjusting is OK in my experience.