I wish I could remember where I read this, so I could cite the evidence. But I can't so take this as a maybe true statement that someone you don't know posted on the internet....
The reason there are so many "chocolate" and "black" diamonds in jewelry today is that these were once industrial grade diamonds. They were used for cutting tools and phonograph needles. We now use lasers for many of the jobs these diamonds were once used for. So we get "chocolate" and "black" diamonds touted as the "hot" thing for jewelry. They are really more or less industrial grade stones.
OK, here is a link to a statement (go about half-way down the page):
http://www.diamondvues.com/2007/08/
"Cognac" "Chocolate" "Champagne" Diamonds. What Are They?
It's funny how until very recently, diamonds of considerably lower colors with brownish hues and yellowish overtones, were simply known as "low color diamonds".
Lower colored diamonds, are not as scarce or valuable as diamonds of icy white colors and therefore command less of a premium than the diamonds of higher (better) color grades.
Problem was, certain diamond mines tended to only produce diamonds of substantially lower colors. Well these are diamonds too and they needed to be sold..right? Well, of course!
Some brilliant marketing guru came up with an incredible idea; why not market these diamonds with finesse! Indeed, why not turn the very liability of the stone into something positive?
Thus, was born the marketing strategy known as "chocolate diamonds," "cognac diamonds," and/or "champagne diamonds".
You turn the negative into a positive......."
I'm not that into diamonds, but Jewelry Television has some very nice "champagne" pieces.