The blue gene (Bl), which creates the plumage color of a blue Ameraucana, is an autosomal incomplete dominant diluting gene. In its heterozygous form (one copy of the Bl gene), black feathers are diluted to create blue plumage color.
The standard calls for a blue Ameraucana to have lacing present. Multiple scientific studies have found that there are three genes involved in creating the black single lacing on a blue Ameraucana. Those three genes are the Pattern gene (Pg), Melanotic gene (MI) and Columbian gene (Co). The Pattern gene is responsible for creating patterns on plumage. It organizes black pigment concentrically. The Melanotic gene is a black intensifier. It enhances and moves black pigment to the outer border of the feather. This makes the outer border black and double lacing is created (Pg+Ml). By adding Columbian (Co), which is an eumelanin restrictor, the inner laces are taken away and single lacing is created (Pg+Ml+Co).
Blue Ameraucana cockerels are darker in the hackle, back, saddle and wingbows because of their sexually dimorphic plumage.