Having a large outdoor area to play this game is crucial. If the inbounds area is too small it is not much of a challenge for the rainbow catcher(s) and your party guest will quickly become bored.
The Set Up: Select one of your players to serve as the rainbow catcher and ask them to stand away from the other players. Once the rainbow catcher cannot hear, assign each of the other players one color of the rainbow; red, orange, yellow, green, blue, purple. Mark a large rectangular playing area and have the rainbow catcher stand in the middle of it with all of the colors on one side.
The Rules: Play starts with the rainbow catcher calling out a color. All of the players that were given that color must try to run past the rainbow catcher to the other side of the playing area while staying inbounds. Once they reach the other side(untagged) they are safe for that turn. If a player is tagged by the rainbow catcher or goes out of bounds then they also become a rainbow catcher and stand in the middle trying to catch the colors when they are called. Play continues until there is only one color player is left, who is the winner and the rainbow catcher to start the next game.
Clear the Field of Play: As is the case with any active outdoor game, make sure the playing area is clear of anything the party guests might twist an ankle on or trip over.