In the Netherlands the most premium cards are silver/gold, only Amex issue black Platinum cards cobranded with Flying Blue.
I think that it depend on country which colour would be used most, but you are right the standard card would be the most issued card as not everyone choose for Premium
Could you maybe tell us more about what happened with the black premium cards? And if those will return/changed for another colour(or metal) 
Unfortunately, the black cards are currently unavailable however this is only temporary. You will be able to order a black premium card again on the 12th Jan.