Yes I found that too, but couldn't find any evidence of it actually being produced or anybody trying to mix such an alloy and testing it. It all came about when I saw a Goldsmith's photo of some gold she was just about to work with, and I admired the chunk of what I thought was "chocolate" gold. Turned out it was just the lighting in the photo and the piece in question was in fact white gold! She said she'd be interested in such an alloy if it exists, so I said I'd try and find out. As far as I know, any products I've seen on the market that have had such an appearance, have been merely surface coated, the coating having been applied by CVD.