Blue for drops (smoking meat in villages, drying meat in the wilderness, lightening load when engaging big game or Njerpez, raft left on waterways)
Red for danger
Yellow for noting village/settlement fine&masterwork goods, sage, animals.
Green for worthy plants (burdock, bear pipes, golden rod and so on)
White for any other notes.
I like that you can F6 in zoom in view, make note, chase game, get kill or not. Get on wilderness view and check where you left your stuff. Super handy when bumping into game blindly.