Here's the recipe for the Colonel's original herbs and spices seasoning:
https://www.chicagotribune.com/2016/08/19/kfc-recipe-reveale...
https://www.chicagotribune.com/2016/08/19/kfc-recipe-reveale...
My main takeaway (PNI!) is that the white pepper and the smoked paprika together are the heart of the KFC flavour. The rest just augment, refine the flavour. And of course, the salt and/or MSG go a long way.
These Glen and Friends Cooking videos of North American cuisine development are top notch.