The swap rule in Hex is an optional feature used to balance gameplay when one player has an advantage due to the first-move advantage inherent in many turn-based games. It allows players to switch colors at any point during the match instead of solely relying on asymmetrical starting positions favoring one player over another. By offering this choice, it helps to mitigate or even out any positional advantages associated with going first or second by allowing players an opportunity for a tactical shift mid-game if they find themselves in a disadvantageous position initially. This rule adds an extra layer of strategic decision-making and helps ensure fair gameplay by reducing potential bias caused by starting positions alone.