The name bluebloods refers to the pallor of the Spanish ruling classes after the conquest of the darker skinned Moors.
After the blood in them loses oxygen while flowing back to the heart, the veins of fair or untanned people whose skin is never exposed to the sun appear blue.
The veins of those with darker complexions, however, like the Moors, are less obvious.
Their blue blood distinguished true Spanish aristocracy from the conquering Moors.
