Black Forest Prime Rib Rub

I was in SW Michigan this week and a friend there mentioned that he ordered a prime rib with black forest rub for Chrismas dinner. It is his family's favorite and they have it every Christmas.

He thought the rub was specific to his butcher, but we later saw the same thing at a grocery meat counter. That butcher did not know what was in the rub and didn't even know the main ingredients. The rib roast in the meat case looked like it was soaked in soy or Worchestershire sauce, almost pure black.

Does anyone have a recipe for Black Forest Prime Rib or know what the main ingredients are?

At a meat market called Schaub's in Palo Alto, CA, they sell a tri-tip called "Fred's Steak" that's marinated in something that makes the meat black as coal. There is some conjecture that the blackening ingredient is something like Gravy Master or Kitchen Bouquet along with soy sauce and other spices.

Also, here's a recipe I found on cooks.com for something called "Black Beef".

3 lg. onions
3 cloves garlic
1 c. soy sauce
2 tbsp. mixed Italian herbs
1/4 c. Kitchen Bouquet

Place all marinade ingredients in blender. Blend until smooth. Marinate meat overnight.

Regards,
Chris