Aw, here I was all excited about some sort of thermochromic glass that changed colors when heat was applied or something, but alas!
like glass pipes that get colorful when they've been smoked for a while
The glass doesn't actually
change colors, it's just that the colors that are in it already become more visible when all that tarry gunk builds up inside the pipe and makes a nice black backdrop for them to be viewed against. That's why they put that black felt underneath them in the display cases at the smoke
shop. If you want your glass drip tip to change colors, try smoking some
tobacco (etc.)
through it, that should ought to do the trick...
Source: I've become familiar with these glass pipes of which you speak, and the colors always disappear after a thorough cleaning.
