They probably have White Leghorn, along with Silkie or Cemani, and likely some other things as well.So it's safe to say, for a more "Zoomed in," idea, these are likely a California Grey with either Silkie or Cemani blood/ancestors?
Because of what color your birds are, I think White Leghorns are much more likely to be involved than California Grays.
It is genetically impossible to get that color chicken by crossing Ayam Cemani (black) with California Gray (black with white barring). But crossing Ayam Cemani with a White Leghorn or a California White could make a chicken like that picture.I had one that looked like that is was an ayam cemani/california gray mix.
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