No. NTB... It is assuredly not just you... and I don't mean to criticize anyone individually. But in fact there has been a steady pace of people posting chick pics of birds that were either crosses or anomalies from alleged purebred parents. Some birds were perhaps just poor examples of Marans, the color was off or the type was poor..... but some birds were obviously crosses. Pendenesencas causing white ear lobes..... yellow skinned birds showing as green legs... (these are things I myself experienced and culled). One of those chicks I saw in an earlier picture reminded me of a Barnevelder which would be another bird that lays a very dark egg, that people might be crossing in.
People are getting birds from E bay or other places.... and there is no recourse or quality control other than the sellers integrity.... and when they are selling the eggs for 50 dollars a dozen or sometimes more, there is likely a motivation to present darker eggs. My birds lay some pretty dark eggs, but they also lay some lighter ones, and some speckled ones.... There could well be mixed heritage in my own birds... but it would have to be 8 generations back now... and it wouldn't be from anything I introduced..... and I never hatch a "mystery chick". I do see some variance...(knock on wood) but not the variance some people are finding. I will get a bird with too much halo, or comb sprigs, or maybe some straw colored hackle instead of copper.... But never something that I cannot identify.
And I think the reason for this is there are crosses that are not known to the owners of the stock. And of course there are people that are just saying ... "I want to cross in some barnevelder or some Pendenesenca, and then breed back to BCM for two generations or three generations.... and the anomalies are in there. . They are mutts. Black Coppers are no different than any other chicken.... if you introduce crosses, they are no longer Black Coppers. But truly... look back through the posts... you will see what I am talking about. It takes alot of time to breed true for any bird breed, and people are muddying the provenance of their own birds... which is their own business, but don't be surprised that no one can identify these birds from a photo other than to say....well, I suspect the serious BCM people usually just say nothing.