[freedom44]

Iranians back then including Darius the Great who had light skin and blue eyes as light as the sky according to historical accounts were light featured. Iranians today due to the Arab invasions around have a mix of European and Mid-eastern features.

[Prost1]

Iran was also an important trade route with China, India and the Turkish provinces.

Thus, there is a mixture and the darker skinned are most likely from the Dravidian stock of India who are prevalent in Southern Pakistan (once India).