The 5 colors of mana - white, blue, black, red, and green - are the building blocks of the universe, of which everything can be described as falling into one or more of the categories. White mana represents soldiers, holiness, life. blue mana represents air, sea, and magic in it's raw state. Black mana is the color of death and all that is unholy. Red mana represents fire, rock, chaotic might. Green mana is the color of wildlife, plants, and nature. Eldrazi are the only things that do not fall under one or more of the categories- they are devoid., which makes them extremely dangerous.