There is a set area of play, and a facilitator who stands on the centerline of that area. The facilitator will say a color, and if a child is wearing that color, they are free to cross the field. If a player is not wearing that color, they must run to cross the area of play. The first player to be tagged by the facilitator is the next ‘gatekeeper’ (the facilitator).
Variation: Substitute colors for something else (ex: If you have two siblings, cross the field, etc.)