I wondered about that once myself, but instead of asking I took direct action and took apart a tube to see what was in there and I found out how it's done.There's a plastic gizmo in the nozzle that looks like a funnel, the wide end is as big around as the nozzle opening, the tube part of the funnel is about an inch long, and there are little holes around that top of the tube where it attaches to the funnel part, up at the top where the colored stuff is. There is about an inch of colored toothpaste reaching almost to the end of the funnel tube then the rest of the tube is filled with the regular stuff. When you squeeze the tube ( from the bottom from the bottom! dang you middle squeezers!) the white stuff goes through and out the little tube, the colored stuff goes thru the little holes and it comes out all stripedy. Back then we only had Stripe brand toothpaste with red stripes, now I see there are multi-colored stripes. I haven't taken one of those apart. I imagine there is a layer of one color with its holes and another layer on top of that with its holes a bit higher up. If you decide to investigate, let me pass this on; Mom reminded me that I could have found out just as much by dissecting an empty tube as the nearly new giant family economy size one that I examined. Mom had a curious way of reminding me of things that involved a bedroom slipper and me bending over. Ahhh, sometimes the path to scientific knowledge is a painful one. It did make a neat gloppy mess in the sink though, by the time I got it cleaned up the sink was reeeeeeeal shiny and smelled minty fresh.

with a stiper machine

theres more than one compartment in the tube.