While "Black Hills Gold" is a jewelry company, you are not correct in saying there is no such thing as actual black hills gold.
I personally, have, in my possession, 3 peices, dug myself of gold which has a bluish, a greenish and a reddish tinge. (used to live in the area).
These are from about.com site:
Black Hills Gold Black Hills Gold
Legend says that a French goldsmith named Henri LeBeauold first created this jewelry after a dream. Traditional pieces are designs of leaves, grape clusters, and vines, and are made with a combination of green, rose, and yellow gold.
Definition: A style of gold jewelry said to have first been created in the 1870's by a French goldsmith named Henri LeBeauold, who is said to have dreamed about the design after passing out from thirst and starvation. Black Hills gold jewelry depicts leaves, grape clusters and vines, and is made with a combination of green, rose, and yellow gold.
The jewelry must be manufactured in the Black Hills of South Dakota in order to be called Black Hills Gold Jewelry
The Black Hills Gold Company DOES add silver, etc., to their jewelry - first, to give it that expected look, and, to make it more durable, and for decoration sake.
But that is not to say that the pinkish tone (or greenish tones, etc), are not naturally occurring in that area.
One thing about gold, it's origin can be discovered, just by the way it looks.
Hmmmmmmmmmmm- I love gold!!!
B