i have never seen yellow smoke and i have a pipe that is basically impossible to clean, and it holds a decent amount in it if you dont clear it, so it is easy to get stale. i can get it concentrated in there very easily by hitting it hard with the carb totally sealed. never once have i seen yellow smoke. im not calling any of you liars, im just saying it isnt something that happens any time you hit a dirty pipe, hit stale smoke, or take a big concentrated rip.