Remember that festivals have a theme. Harvest season has the reaper and thanksgiving stuff. All hallows eve has costumes. Etc. Flood festivals would have everybody carring festive umbrellas or parisols. Colors of storms(grey, smoke, fog colors), as well as colors of after storms(rainbows, sunbeams through clouds etc.) Remember the gods of weather at this time too, and what would please a storm god. How about people on stilts dressed as storm giants??