Loras Tyrell. . .

[The Roaring Bear]

Well I mean it depends on the context right? For instance, a rainbow on a bar sign that homosexuals frequent indicates that it is a gay bar and a rainbow colored Volkswagon beetle (with "fagbug" printed across the side) is a symbol of gay pride. Notice its kindda like the rainbow indicates it by association? Itis similar when you have two male characters that obviously care deeply for one another, mixed with jests made about them exploring one another, and then them choosing a rainbow cloak as their symbol that kindda directs the meaning here.

[Ser Malthred Storm]

I had ignored the various cited remarks about Loras and Renly, though taken all together the make a good case for them being homosexual. Altouhg it's unlikely Margaery will die a maid if an heir is needed. Quite a few gay men are fathers, and a stand-in could likely be found if necessary, maybe one of Robert's bastards to keep it in the family.

Regarding the rainbow symbolism, it must be a generational thing, 'cause I don't associate rainbows with homosexuality. More with Jesse Jackson's Rainbow Coalition, pots of gold, even the end of the Biblical deluge.

So those unicorns pissing rainbows are gay symbols?

The Rainbows in ASoIaF are part of the religion of the Seven.

[Ran]

What Ser Malthred said. In fact, the rainbow does mean something in Westeros -- it's an emblem of the Faith, introduced in the very first novel (the rainbow hues in the sept at Riverrun, the Rainbow Pool outside of Baelor's sept). That, and the fact that it was colorful, fitting the pagentary Renly enjoyed. The Warrior's Sons, one of the militant orders of the Faith, has a rainbow sword as its sigil.

Again, as noted, GRRM didn't intend that suggestion at all by using it. For him, it just fit the worldbuilding. The notion that he automatically associates rainbows with the LGBT movement is almost certainly erroneous -- he's a baby boomer who grew up in New Jersey, not a Gen-Xr from San Francisco.