Bright colours attract bees, bumblebees and wasps, especially yellow and blue:
http://resteasypestcontrol.com/bees-and-wasps-facts-which-colors-will-attract-them/
http://animalquestions.org/invertebrates/bees/are-bees-attracted-to-certain-colors/
But in your case, it might be a migrating swarm, and the green with the players' coloured clothing might have looked like a meadow with big flowers.
Bees are atteacted to a color spectrum largely undectible to the human eye.
