In the book Last Days of the Incas on page 187 it says:
Visiting the royal court in Valladolid, Hernando (Pizarro) had then conducted a deft negotiation with the King. As a result, King Charles had subsequently granted the Pizarros the right to transport two hundred tariff-free black slaves to work in Peru's mines, the right to import four white female slaves...
Where would these white female slaves have come from? In the book he's not quoting anybody else, just stating what Hernando was able to get from the king. I was just wondering where the white slaves had come from. If they were really slaves, or just lowly servant girls.
Before the trans-Atlantic slave trade institutionalized race-based slavery in the west, the majority of slaves in (Christian) Iberia were Iberian Muslims captured in war and their descendants. In the area around Valladolid, according to William Phillips, that would account for the vast majority of slaves through the fifteenth century.
Where Pizarro was from (Trujillo) and its environs were more closely tied into the circum-Mediterranean slave trade. Phillips found one set of records from 15th century Catalonia that enumerated one town's slave population. They consisted of claimed Mongols, North African Berbers, Spanish Muslims, sub-Saharan Africans, Canary Islanders, Russians, Bulgars, and Circassians. So Eastern Europe might be another possibility for light-skinned slaves in the sixteenth century, although a numerically less likely one.
Of course, without seeing the original info, it's tough to know in what sense MacQuarrie is using the terms black and white. :/ Although "black" and "white" are descriptions generally linked to stereotypical phenotype of Muslims and Christians in the late Middle Ages, visual evidence from Spain suggests that actual perceptions differed from religious/literary rhetoric. So I think we have to be very careful before assigning too much weight to those terms, one way or another.