Hypertext, is a word or graphic which is linked to another page. Clicking on the link will take you to the new page. Hypertext, commonly referred to as a link, is usually shown in blue, but can be in other colors as it is on this page where the hypertext links are green.
This is a link
Links which have been clicked on (or followed) are usually shown in purple for a period of time unless the color has been changed by the programmer or user. In this tutorial, followed links are shown in yellow. The length of time a link remains purple (or yellow) depends on the way your browser is setup. If your followed links are not changing color it is because of your browser's setup.