Kenny & Harley
Kenny probably wouldn't have noticed if he wasn't on acid. He never really did noticed things like that unless it was a big change that was noticable. Something like changing to a completely different color or cutting it all off. But something like a trim? Yeah, he probably wouldn't have noticed.
Since Harley only redyed her hair, he probably only noticed because of the acid. "No, I'm totally fucking tripping right now," he grinned at her, still playing with the pink tip of her hair absentmindedly.