The color used links turn is (probably) the result of settings in your browser, rather than TMP.
It is possible for a web page to use a thing called "style sheet" (a set of defaults for how to display things like regular text, headlines, paragraph indents, etc. -- like a Manual of Style the browser enforces on plain text) to change the default color for visited and non-visited links. It is unlikely TMP does that; very few people do it because it is crappy and annoying.
It is also possible that you changed your defaults, which you can do. Given the plethora of stupid things that "modern" browsers do for you now (because the programmers think the mass market is too stupid/lazy to do things for themselves), it is more than just possible.
That tripe above out of the way, the most likely thing that happened is you accidentally cleared the cache on your machine that knew what you had and had not visited on TMP. See above comment about nice programs that "do stuff" for people.
As to why your visited links are "pink" instead of purple (the default), it could have to do with the machine's color settings (especially if you only see the effect on one specific computer). Is it pink-pink or more magenta-trying-real-hard-to-be-purplish-but-just-not-pulling-it-off (which is the color I use for Mind Flayers…)?