In Magic: The Gathering there are 5 colours. Each represent a certain element in the world, a certain attribute, and a certain style. To win against an opponent, players build decks using 1-5 colours. Since each colour has its own style, they can interact with each other and can oppose other colours.

Here are the 5 colours in Magic: The Gathering...

White represents a Plains and life
Blue represents an Island and knowledge
Green represents a Forest and nature
Black represents a Swamp and sacrifices
Red represents a Mountain and speed

Using these 5 colours, players choose which ones interact well with one another in order to win against their opponent's colours. All of these colours have enemies and friends.