I think some did have spots of brown on their heads!Most of the time I cannot tell Tri-color Mottled Slates or Mottled Slates from Blue Slates at the hatch. Sometimes but not always they may have a spot of brown on their head if they are the Tri-colors.
I have seen the different varieties stick to their own variety when free ranging but all bets are off during breeding season when the dominant tom will breed any variety.
It’s also complicated by what I believe is the chocolate gene showing up in some of the poults. (Father must have been split to it, the poults in question would be females.) There were 3 if I remember correctly w/o checking my notes. 2 greyish-brown and 1 lighter greyish-brown. I still have the lighter one, which I assume is chocolate lavender. I should get some pictures to see if she is tricolor mottled.