The Five Main Colors

Mana is what all magic is based on, and Mana comes in 5 different colors. These colors fit certain models of morality and dogma. While MTGTT has no morality system, players are expected to behave within the philosophy of their color(s).

White
White puts value in the group, the community, and its civilization as a whole. White's ultimate goal is peace, harmony, and perfection — a world where everyone gets along and no one seeks to disturb the bonds of unity that White had worked so long to forge. To govern and protect its community, White makes use of and puts value in a number of broad concepts; morality (ethics, grace, truth), order (law, discipline, duty), uniformity (conformity, religion), and structure (government, planning, reason).

Blue
Blue is the color that looks on the world and sees opportunity. For Blue, life is a chance to contemplate oneself, and what is possible, and to bring about the best of both. Implicitly, in that general world view, Blue believes in tabula rasa: it sees in each thing, the potential for being anything. One need only understand how, to make the change. So with this ill-formed goal before it, Blue reasons that if it is to make itself better, it must become capable of everything it could be capable of, for that is to "merely add" to its own capabilities. Blue believes it can't possibly be bad to acquire the potential for any conscious action. Thus, Blue, believing it is capable of changing anything if it understands the change, and believing it is imperative that it acquire every capability it could have, concludes that it is imperative that it understand change. Moreover, Blue decides that it must understand everything; for truly, understanding can only improve one's effectiveness in any task. To gain understanding, Blue must acquire knowledge. Since knowledge itself will inform every other decision, Blue forms its principle goal: omniscience, the knowledge of all.

Black
Black is the color of self-indulgence, parasitism, amorality and unfettered desire for power. It believes that the world is made for its taking and that the weak exist to be exploited by the strong. The essence of Black is to see one's own ego as so supremely invaluable, that the prospect of enslavement, of subordinating that ego to another, is utterly inadmissible. So, to be in accord with its perceptions and beliefs, Black simply must discard all obligations but to acquire power for itself. It can be no less than the one supreme being who is subordinate to no other, the possessor of all power in the universe - it must become omnipotent.

Red
Above all else, red values freedom of expression. It wants to do what it wants, when it wants, to whom it wants, and nobody can tell it otherwise. It believes that life would be much more fun if everyone stopped caring about rules, laws and personal appearances and just spent their time indulging their desires. This leads into red's other core value: chaos. Red sees order of any kind as pointlessly inhibiting, believing that only through embracing anarchy could everyone really be free to enjoy life to the fullest. Finally, red is the color of immediate action and immediate gratification. If it wants something it will act on its impulses and take it, regardless of the consequences.

Green
Green is the color of nature, growth, interdependence and instinct. It believes that obedience the natural order alone is the best way to exist and thus favors a simplistic way of living in harmony with the rest of the world. This can often lead to it be perceived as a pacifistic color, as it does not seek to make conflict with the other colors as long as they leave it alone and do not disrespect nature. However, it is fierce when it feels threatened and can be predatory and aggressive if its instincts dictate.

Source
http://mtgsalvation.gamepedia.com/Color