Umber is explained by CyFi as a word invented to describe the African race. The inventor of the word was a mixed-raced artist who got famous for painting people of African ancestry in the Deep South using the color 'umber' most. People liked that a whole lot better than "black", so it just stuck.
Sienna eventually became the term used for so-called "white" people, after another paint color. Although both terms no longer have a value of judgment to them, racism has not gone completely, but it had improved with these new terms.
ChanceFolk, a shortcut for People of Chance, rudely known in slang as SlotMongers, are Native Americans. They get their title because of their known luck and business in gambling. These people, once lived in America, are now divided into different tribes separated from the outside world by high walls and kept in their rez, or reservations. They do not favor unwinding humans, so they use their belief in spirit-guides as their salvation for health problems: instead of obtaining human body parts through unwinding, they use animals', particularly a person's totem animal, instead.