The card number cannot designate the color of a USA-issued charge card because the number may remain the same when you change between Green, Gold, Platinum. Not sure about Centurion.
When I asked the AMEX people about this a few months ago, (downgrading my plat amex to a gold) they told me that I would not keep my card number and that I would have to apply for the gold as a new card and then just cancel the plat, is this true?