Magic the Gathering has five distinct colors used to determine the strategy or overall theme of Gameplay. These colors are:
Focuses on healing and restoration, with the ability to utilize many smaller creatures quickly.
The power of control. Blue is all about not letting your opponent make his moves, and insuring your own. It also boasts some of the best draw power in the game.
The color of death and decay. Black is about one thing, and one thing only: Winning. Even if it means having to hurt yourself in order to hurt your enemy more, or to hurt yourself to get more.
The color of fire. Red has the ability to burn through your opponent's Life quickly, and mercilessly.
Most of the time while cards are on the battlefield, the color of cards isn't that important. At many times, however, color is very important. Many cards have protection from certain colors, and others can't be blocked except by creatures with the same color as them. Many black spells can only destroy non-black creatures.
Colorless cards have none of the above 5 colors in their cards cost.