Going by the ABA standard hackle should be similar to a blue red OE. So a shade between a bb red and wheaton. I would say it would be a hard color to recreate with a paint brush. Judges interpret the standard just as we do. Place 5 cocks of equal type one weekend and the next weekend a judge will place them in reverse based on color only.
I always thought nankins were darker; more like a New Hampshire or ginger red. BUT I was wrong.
That's just the males, I have no idea on the females.
I don't think the standard should be changed to what we have today...that's to easy. Even breeds such as the Plymouth Rock standard is nearly unachievable without loosing something, you gain one strength but traits are linked in some way and you end up breeding away from another.
Just my opinions of course. Nice pictures Charlie