Considering the painting is illustrating a scene from A Dance With Dragons, and has nothing to do with Renly at all...

(I don't want to put spoilers here in case you haven't read the books. Though if you have, that's "Reek" at Moat Cailin.)



Also, while GRRM did say he intended Renly to be gay, he also said the Rainbow Guard was not supposed to be a clue, it was just a coincidence. (He was kind of oblivious to gay symbols at the time.) He intended the Guard to be a contrast to the white cloaks of the usual Kingsguard and the black of the Night's Watch, using the religious symbolism of the Faith of the Seven.