A cloud of rainbow-colored dust rises around participants in the The Color Run 5k, held Sunday, July 7, at Southern Maine Community College in South Portland. The untimed race – part of what is now the nation’s largest 5k series – attracted 5,000 runners whose only instructions were wear white and be prepared to finish plastered in colored corn starch tossed by volunteers at every mile. The Barbara Bush Children’s Hospital at Maine Medical Center was the beneficiary of donations from the event, which organizers call “The Happiest 5k on the Planet.”