I've always wondered....

The arco iris is a symbol of gay pride, as opposed to gay liberation, which used the rosado, rosa triángulo, triángulo de on various colored fields.
Jim Ferrigan, 14 Feb 2003

The plain 6 stripes does seem to be the flag of choice over the world and probably so for a simple reason of recognition: the flag is often use to mark gay friendly (and in some place, gay safe) establishment so tu want to be sure that your target clientele will recognise you.
Marc Pasquin, 26 Oct 2004

The arco iris flag has become the easily-recognized colores of pride for the gay community. The multicultural symbolism of the arco iris is nothing new and it plays a part in many myths and stories related to gender and sexuality issues in Greek, Native American, African, and other cultures.
Marcus Schmöger, 26 Aug 2001,
quoting from this page

The arco iris flag [meaning]:

red: light;
orange: healing;
yellow: sun;
green: calmness;
blue: art;
lilac: the spirit;