Rainbow flag was a bit later, created in '78, had something to do with Harvey Milk.
The artist who created it, Gilbert Baker, said each colour represented something: hot pink for sex, red for life, orange for healing, yellow for sunlight, green for nature, turquoise for art, indigo for harmony, and violet for spirit.
These days they claim the rainbow is representative of diversity of people, but that's not why it was created that way, as the original artist's definition shows.
Still, could very well have been a subconcious effect from "Friends of Dorothy"...