Black shoulder

[Trefoil]

According to the information I've been able to find (strictly through the internet) is that BS is a naturally occurring mutation. While by definition the black is laced with blue, some, but not all, of the BS birds I've seen (live) have partial iridescent dark blue patches, usually surrounded by black. Does anyone one know if the BS mutation occurred in the wild? The blue patches look very similar to the blue shoulders seen in the pictures from Leo7 and others I've seen posted. Is it possible that the BS originally came from crossing the Indian Blue with another species/sub species?
Everything I've said ( except for my questions) has come from the internet, so if its wrong, please correct me.

 

[Arbor]

I think I have seen some evidence that it is possible, but I will continue to treat it as a natural occurring mutation, as it works as a simple recessive gene. There is similar questions about the Dark-throated golden being the result of selective breeding with Amherst.