I have a flock of Splash, Blue, Blue Copper, Black, and Black Coppers in a mixed pen. I've managed to hatch about half a dozen Columbians that came thru.
I got columbians when I crossed a Blue Tailed Buff Marans roo with a Silver Cuckoo Marans hen. This was most curious, so I've done a huge amount of googling, and asked questions at the MCCUSA forum (US Marans club). I think I have a pretty good handle on understanding how this happened.
To begin with, Columbian Marans are more properly called Ermines.
Coumbians are partridge based. They have a colored saddle and a gray undercolor.
Ermines are Wheaten based. They have a white saddle and white undercolor.
Genetically speaking, Ermine Marans are Columbian Silver Wheaten (eWh/eWh Co/Co S+/S+) and Black-tailed Buffs are Columbian Gold Wheaten (eWh/eWh Co/Co s+/s+)
To address your specific experience, Black Copper are genetically Brown-Red. Brown-Red can be partridge or wheaten based. Specifically, Black Copper Marans are wheaten based.
Black Coppers can and do throw Wheatens. Black-tailed Buffs (or in my case, Blue-tailed Buffs), often throw Wheaten.
Keep in mind, Ermine is Wheaten based, so if you have Wheaten based chickens, you have the potential for Ermine.
Ermine is silver factored. Silver Cuckoo is silver factored.
BT Buffs and Black Coppers are Gold Factored.
To get Ermine, you have to remove the gold (else you'll have BT Buff).
In my case, the Cuckoo hen carried the silver, and the BT Buff carried the gold. This is a sex link cross, and all my ermines from that mating were males.
In the case of your Ermines, I don't know which was the father and which was the mother, but you would have had to have a silver factored bird in the pen. Perhaps your splash, blue or black carry silver?
I have put one Ermine male back with his mother, and I have eggs in the incubator now. I'll put pullets from that mating with the other two males. Here's hoping I can get these going. They are beautiful birds, and the original hen lays a dark egg. *crossing fingers*
