Breed a male with one copy of the gene with a cuckoo female and you will get males with one and two copies of the gene and both cuckoo and black females. Breed a male with one copy with a black female and you will get cuckoo (one copy) and black of both genders.
Yup, it most likely came from a cuckoo rooster. But it will not be able to pass the gene for cuckoo to its kids. You can still use it in your project, but it will be the same as useing any other black colored silkie in the project. No extra hidden advantage.
Sonoran answered you above.
thanks for finding him, I'll post pictures of his two brothers and two sisters I was lucky enough to hatch out. But one is a silver cuckoo roo, one pure red silkie roo, (the roo in the picture abouve red black and white stripes so i've been calling him creole)one chocolate hen and one light red cuckoo hen, it was almost 2 years ago and i was very new to hatching, plus I'm sure the quality has improved, since my cockoo's all have red combs, and lighter skin. There was also one very lovely porcelain cuckoo roo that was breath taking but of course that the one a hawk go's after
. My new sizzle babies ( not from the mail order eggs) almost all have dark skin and combs. But I hear that sometimes fades with time? Plus two years ago the eggs he was selling where $100 for 3 dozen. Instead of $250 they are now. I highly recommend them but I'll have to wait for a big pay day to afford them again 
