I’ve got a computer here that’s showing sites and fonts as completely different from what they should be. Example: A site with a black background and Verdana font shows up as a site with a white background and some other font.
Is your text coding set to Western European (Windows)? You can check it by going to the View menu and highlighting Encoding. I know if I use a computer in the library the coding is often set to Chinese or Japanese character sets, which can make things look a little weird.
If you are at a public terminal, like at a library, the accessibility settings in the browser might be set to high contrast by a user with vision problems, and others don’t realize it to unset the option.