Please, decide if it's a kingdom with a king and royal orders, or an empire with an emperor with imperial orders.
This is hella confusing, because you say Blanche kingdom with king, then throw in an imperial order 😐
And I agree with the others, 300 years may sound a lot but actually, it's not a lot in a people's history. And yeah, uh, the skin tone is one thing, but you can only have red hair if both of your parents have at least the dormant gene for that if I remember correctly. And I think it's actually the rarest. (Which might not mean much since we're in a fantasy world, for all I know, 70% of the population might have red hair. Okay, probably not, seems like only the Leta people have red hair here??? Maybe that's what the Blanches are using to distinguish them?)