The fantasy card game Magic: The Gathering contains 5 factions, called "colors" for balance purpose each with their own individual strengths and weaknesses. However these 5 are not different purely in gameplay terms. Each of the 5 Colors also holds their own philosophy and psychology such that they are also make for a convenient way of expressing your identity online. The 5 Colors have their alliances and enemies (2 each), their own combinations and conflicts, and their own arguments and real world analogies to support their argument.
Now of course any real person has at least a little of all 5 colors, what color you are or a character is, is question of what color they are the MOST. Because of this you can also talk about a person in terms of multiple colors, listing the colors they have the most in order. Their is more logic to this, but for the most part this post will stick to mono-colors. The Essential Nature of Each Color, as well as their relationships was first codified in the classical MTG Color Wheel:
Confused at parts? This is common and there has been much contention over the internet on what various parts MEAN. The colors were even more strictly defined by Mark Rosewater (the person in charge of keeping these things consistent) here: