Yes, you're right. There is another tier of membership after Platinum and the card is black-ish in colour. I think they call it it Platinum Premier Elite or something. This is sometimes referred to as a "secret" level as it is not widely publicised. As far as I know, there is no official qualifying criteria but over 120-125 nights per year should do it and I think it may be at the hotel's discretion. I don't think you necessarily get much more in term so f benefits compared to platinum but probably have a better chance of upgrade. Hope that helps!
Reflecting on andrews comments:
You wont find an official requirement for Platinum Premier publicised ANYWHERE, from any official Marriott DNA, as it is a moving target every year, supposedly the top 3% of customers. But no one knows for sure if it is the top 3% in spend, or top 3% in nights, top 3% for both. You will never know until they do it.
You will get a Platinum Premier Card.........and a trinket the year you qualify, could be a solar powered charger, could be an amenity kit, could be a subscription to the online WSJ for a year, could be a Pet Rock next year, or maybe something you would use, .....or not. You will never know until you get it.
I know people that have stayed 200 nights in a year, and did not qualify, and I know people that have spent $30,000 in stays, and have not qualified. I personally have stayed 110 nights in year and made it, and in another year, I spent 176 nights, and not made it.
Nothing special as far as differences at most of the hotels in the way they treat Premier's -v- Plain ol Platinums, there are no Marriott posted extra benefits between the 2 levels, except a different, super duper, (gang sign and handshake required) special phone number, where they only put you on hold for 17 minutes instead of the usual 18.
I was Platinum Premier for many years until I quit staying at Marriott's in May 2012, when the benefits started eroding worse than ever.........(they continue to).
Now I have reverted back to a Lifetime Platinum.
whoaaaaaaaaaaaaaaaaaa is me...................dont know if I can live with myself