Less rare. I've gotten half a dozen purples and haven't seen a single white-black.
The fact is: the OP wants something very rare for cosmetic reasons. Everyone wants this crystal for cosmetic reasons. It has a very high demand and a very low supply, therefore ppl can charge pretty much whatever they want for them.
Quoted for truth.
Really, OP, the fact that people 'could' get the same stats for less credits undermines your argument. If you just wanted it for the stats, then you could get a different, cheaper color, too.
If you want it for cosmetic reasons...well, join the club. Simple economics: supply and demand. Aesthetic demand is what keeps the price so high.