firstly i would like to encourage caz1974 and otrere to seek phyciatric help as soon as possible....
secondly: i have a readers digest book called "how is it done" which has loads of questions like these. i will tell you what it says but in super-quick-short version.....
there are 2 methods of getting stripes.
in one of those tall, verticle containers the white and coloured paste get put in seperately and just combine when the paste comes out.
in a traditional tube the coloured paste is in a ring near the tip and when squeezed it goes through tiny holes causing stripes.
good question and i must ask tradey if she gets a lot of free toothpaste? hehe