However, Harry can see every other magical effect just fine; he has no problem with the Avada Kedavra or any of Voldemort’s special effects.
He doesn’t see anything a Muggle wouldn’t see. There’s no reason to think the green light part of Avada Kedavra is magical.
In canon, it seems to be visible. to Muggles. The scene where Voldemort kills the Riddle House caretaker seems to imply that (although not fully since it turns out we are getting the scene from Harry’s mental connection to Voldemort).
He doesn’t see anything a Muggle wouldn’t see. There’s no reason to think the green light part of Avada Kedavra is magical.
In canon, it seems to be visible. to Muggles. The scene where Voldemort kills the Riddle House caretaker seems to imply that (although not fully since it turns out we are getting the scene from Harry’s mental connection to Voldemort).