Excellent observation! "dark skin is sex linked" does get passed around but really, it's missing out on important details. Dark skin is not sex linked. That's exactly why you had dark skin in both sexes... that's to be expected because dark skin inherits in a simple dominant manner.
One very important factor are other genes- one being Id, it inhibits skin pigmentation in the skin. It's the cause of yellow or white legs on birds without barring. This gene will variably repress the dark skin gene. Id is also sex linked.... so a mating of a dark skin with a bird having the Id gene will seem to prove dark skin is sex linked but that's only an illusion because it's the Id gene doing that work.
A dark skin rooster bred with a hen with Id will seem to produce dark skinned daughters and light- light-ish skinned sons. (this will seem to confirm dark skin being sex linked but it's really the Id gene that's sex linked and repressing the skin color in the sons)
A dark skin rooster bred with a hen without Id will produce dark skins in both sexes. Sex linked theory of dark skin simply disproven.
Of course that's just the clean, easy answer. The truth is there's a lot of many genes that can affect how dark the skin gets on the birds. Barring will also affect skin pigmentation, probably some colors/patterns plus if the bird is birchen, wheaten or red duckwing probably has an effect, could be why there's a relatively limited color range in silkies- too many colors pose a challenge to maintaining the dark skin... I don't know all of them but, testerone will lighten the skin on many cockerels when they start to mature. It's always a challenge to get nice dark skin on roosters past one year of age, comparatively easy on hens. This might seem to confirm the idea it's sex linked but it's really sex influenced, the same thing that makes roosters grow rooster feathers and hens don't.
Thank you for you explanation on this, especially the easy way! It really helped alot to understand why this happens! Cuckoo silkies are very hard to keep dark. Thank you!
RIP Sweet Honey! My blind girl who didn't survive the flooding Sept. 2011. You will be very missed by all!!! Honey is my avatar.
Currently have NN's, brown leghorns, salmon favorelles, showgirls and more silkies than I can count!