having a sun tan, was associated with field laborers, so rich people of the time did every thing they could to retain the whitest of skin to demonstrate their richness. When you have very pale skin the veins are more easily seen which carry un-oxygenated blood back to the heart, giving a blueish hue.
Of course, now the term blue blood, just means wealth that has established generational history.
Of course, now the term blue blood, just means wealth that has established generational history.