The music producer posted a pic on social media Saturday in honor of the first day of Pride ... wishing his followers a happy holiday -- and sharing a pic of himself naked, legs dangling in the air.

On top of the pose, Diplo added a rainbow to the pic ... and, it's pretty clearly blasting right out of the guy's booty.

It's a pretty hilarious pic -- and, perfect for the month-long LGBTQ+ celebrations. Plus, Diplo revealed last year he's not totally straight.

Remember ... during an appearance on Emily Ratajkowski's podcast last year, Diplo said he'd received oral sex from a man before -- and, while he wouldn't label his sexuality at the time -- he did say he's "not not gay."

Seems he's aligning himself more with the LGBTQ+ community these days ... or, perhaps just showing love to his fans who identify as gay -- either way, Diplo's firmly standing by the community with the pic.