Ayam and svarthona also have fibromelanosis, and single combs. Silkies have walnut combs only, and walnut is a dominant gene. The SOP for silkies is only for walnut.Many silkies have single combs. The fact it's black is even more Silkie - silkies have black skin.
The lack of crest is interesting.
Blue earlobes are very noticeable.