The Ethnic Detinans are a dark-haired people descended from the settlers from the mother kingdom. They colonized the continent that was primarily inhabited by blonds and created a kingdom called Detina.
The people with dark hair were generally called Detinans while blonds were just referred to as such. Anyone who had dark hair was simply Detinan.
The Detinans originally came from the mother-kingdom and discovered a new continent that was filled with blond tribes. They quickly conquered the tribes and gradually put them to serfdom in the North, while most blonds were allowed to live free in the south. In any way, the blond way of life was lost and the Detinan way of living enforced.
When King Avram ascended to the throne after the death of his father King Buchan, he announced the emancipation of all blond serfs. This caused the North, that relied heavily on blond serf-labor, immediately to go to war, with Avram's cousin Geoffrey leading them. However, the northern provinces were eventually defeated and serfdom was abolished throughout the entire kingdom.
People of dark hair in the series aren't actually called as such. Therefore the admin of this wiki have decided to call them 'ethnic Detinans' to sidestep any issues.