Definition:
"Blue blood" is a term from medieval Europe. People believed that royalty and nobility had blue blood. The elite had enough power and wealth that they could afford to have peasants and the urban poor do their dirty work for them. Since the aristocrats were able to stay inside and avoid long hours in the fields (and the sunlight), they were often so pale that their blue veins showed under their translucent skin, thus leading people to believe that their blood was blue.

Additionally, the daily use of silver forks, spoons, knives, drinking goblets, plates, etc. by the Royal families and nobility caused the condition of Argyria, which literally turned skin blue and developed rather pronounced blue veins and arteries.
Scientists now know that the very high use of silver eating and drinking conveyances means that there was a very high transfer of ionic and colloidal silver mixed into the alkaline and acidic foods. Most directly the silver wine goblet could leach 100s of parts per million of silver in the wine.

Nobility:
Read more about Dutch nobility here. In short: Dutch nobility virtually expired after Charles V (1500-1558) became the ruler. In the 15th century, as towns grew and new social structures and guilds emerged, the power of nobility and clergy diminished. Cities created their own autonomy and judicial privileges and appointed magistrates and important council positions, which the nobles had always kept for themselves. This was the beginning of the end of feudalism and the power of knights. A new "Stadhouder" was now the ruler of the land and Dutch nobility virtually expired and what was left was abolished during Napoleon's occupation. However, after Napoleon's defeat the new Netherlands got a new King in 1815: Willem I. He created most of the present Dutch nobility from old Dutch native regents- and patrician families.

In the newly drawn up list of nobles in Holland in 1814, there were not any O.'s (with any of the various spellings) listed.