What colour shirt/pants should i pair this blazer with?
I'd really like a better photo. Looks to be glen-plaid adjacent, hard to tell in that lighting whether it's gray or if the camera is doing odd things, so let's assume gray. Now, that jacket might be smooth worsted wool, or wool/cashmere, or flannel wool/etc, or tweed, and I can't quite tell what's visual texture vs actual texture in the photo.