A good discussion thread on this subject.... http://ameraucana.org/forum/index.php?topic=1733.0It's more complicated than that. I think there are two things being considered.
First, a blue might (does???) carry a pattern gene (genes?) for lacing independent of the blue genes. Someone wanting to breed blacks doesn't want that pattern showing up. I think it can be ever so slightly noticeable on a black bird.
Secondly there is the issue of the base color. From what I understand, the best blues are silver based while the best blacks are gold based. So, if you want the best blacks, you want gold-based blacks, which might not be coming from a blue breeding program.
Now, here's where I can't get answers: How can you tell a bird is gold based or silver based?
I believe--and those in the know, please chime in because I'm just a rookie looking for answers--most Ameraucanas are gold based.
I've asked the same questions in the other breed (Cochins) that I'm working with. I can't get any good explanations there either. Maybe nobody knows. Maybe you can't tell without doing genetic testing.
The blacks I bought from a top exhibitor came from blue breeding since they came from pens that blues and/or splashes came out of.