Hey,
@nicalandia! I've been dealing with dark, dark Blues that look Black in my silkied Cochin bantams a bit this year. I thought I knew what I was dealing with with that because some of my Blues from last year
are on the darker side for Blue, but then one of my 'Black' hens produced Blue chicks with a Black rooster, and on closer inspection I realized that her down is slatey blue-gray instead of the sort of charcoal gray down of the Blacks. She is black enough that she even iridesces in sunlight like a Black bird would, but looking at her chick down, she did look Blue as a baby.
Researching about dark, dark Blues, I came across a theorized allele of blue, bl^d, that is believed to produce these dark Blue birds that look Black. Do you know anything about this allele and could this truly be what causes this, or are there more likely other genes at play that darken plumage coloring and these birds are just normal Bl/bl+ otherwise? I'd ideally like to breed this trait out of my Cochins so that the Blues and Blacks are distinct in them, so I'm trying to figure out the best way to proceed.
This is the 'Black' hen mentioned above.
And her confusing chick down; I labelled her as Black because she was darker than the definitely Blue chicks and when she feathered in she looked Black as well, but you can see I wasn't 100% convinced when I labeled the picture. She's produced several chicks like this as well with a rooster who is definitely Black based on his down and chick down color. So far, the chicks she's produced like this have feathered out to be indistinguishable from the normal Black chicks.
Normal Blue and Black chicks from the same hatch as her, just for the comparison. One thing I've noticed with these chicks is that the Blues tend to have a dark wash on their legs that the Blacks lack, and the chicks that are in between like the hen above have also had this wash on the legs. They all grow up to have proper yellow legs like they should for the breed, though.
And normal Blue and Black hens to compare as well:
Sorry for the picture overload, just trying to include as much detail as possible.