The guide contains the following color markings:
Red refers to NPCs, though it's also used to mark enemies, wild animals and monsters.
Blue refers to names of locations, both the main ones which appear on the world map and the secondary ones, like single houses or dungeon levels.
Green refers to all items which you can find during the game, which land in the inventory upon collecting
Orange refers to Shouts, Words of Power and other skills and spells.
Maciej "Czarny" Kozlowski
Translated to English by Jakub "cilgan" Lasota