Everyone would be happier with Pepsi color. 
BUT, now Rolex tech guys just cannot make such combination. OR, they can do this but with two separate parts blue and red, which are difficult to make it together at color frontier (zone "3" and "9").
Now, the process of making blue/black ring starts from making full GMT ring in blue, then adding metal salts for lower part of the ring to make it black. Simply, part of the ring is turning from blue to black caused by chemical reaction. Tech guys should find the way to make one PRIMARY color from another PRIMARY color. It is not that easy comparing to making NO-COLOR (black) from a primary color (blue). However, I expect next year Cola GMT - red/black, which is the same process of making blue/black.
Bests
Vit