Joe, there's a joke over here in NC about there being so much religious fervor in certain areas that even the Episcopalians (!) handle snakes.
My early years were spent in CA, and this song (as well as the bumper sticker that accompanied its association with the farm workers) is one of my earliest musical memories. Not sure why. Didn't hear it again until I heard Tao Rodriquez-Seeger sing it with Pete at Carnegie Hall many years later, and I've enjoyed sharing it with others since then.
De Colores has another point of usefulness: it helps us not-yet-Spanish-speakers learn a song that we can sing in Spanish without butchering the thing.