Hex is a game between two players. The player who goes first is typically called "Red". Other names for this player are "Black" and "Vertical". The player who goes second is typically called "Blue". Other names for this player are "White" and "Horizontal".
These conventions are not universal; some people prefer White to go first.
On this Wiki, we usually call the first player "Red" and the second player "Blue". We also usually capitalize the words "Red" and "Blue" when they refer to players, but not when they refer to colors, e.g., "After Red played a red piece, Blue played a blue piece".