The most famous of the blue-people, a blue man endearingly named "Papa Smurf," has recently died.

Born fair skinned, freckled and red-haired, Paul Karason developed blue skin later in life, after acquiring argyria, also known as silver poisoning.

Papa Smurf died this week after complications brought on by pneumonia at a hospital in Washington.

In a 2008 interview, he explains how he came to be so blue: at that time, he still lived in Oregon, and he had come upon an ad that promised rejuvenation through supplements that contained colloidal silver. He drank ten ounces of the stuff a day, in a solution that dissolved easily in water.

In the first few months, the health changes were what he noticed first: his acid reflux problem had gone, his arthritis had gone-and it was only very much later that he noticed his change in color when a friend came over and pointed it out to him.

Trivia: Colloidal silver has been used until as recently as the 50s to cure common diseases such as colds and also allergies.

Karson was not alone, as there were many other blue-skinned people all over the United States. Of these, the Blue Fugates were well known, a family in Kentucky who pass down recessive genes that turn descendants' skin blue. The rare blood disorder was inherited from a French orphan, Martin Fugate, who had settled in Kentucky six generations ago.

Another Blue Man is Kerry Green, who lives in Oklahoma. He was born blue, with a serious heart condition that he later recovered from, but he also has the same blood disorder as the blue Fugates: methemoglobinemia. It is a blood disorder in which an abnormal amount of methemoglobin is produced. It is a form of hemoglobin that cannot effectively release oxygen, causing patients to turn a shade of deathly blue.