I'm not sure it really does add that much color...have you honestly noticed a color difference between a non-decocted and decocted beer? Kai did a couple decoction videos showing color differences. What I took from it is that it doesn't add much, if any, color.There's nothing stopping them from roasting a portion of that munich before it goes in the mash. And can still say its 100%
I wouldn't believe for a second that a beer like Ayinger Altbarisch dunkel is 100% Munich II. There has to be some caramunich/debittered black malt in there for color.