Recently I made a form for a client, and on her computer, one field in the form was showing up with a yellow background. I checked it on 4 different browsers on two different computers in our office, and could not duplicate the problem. Argh! So today, I finally hit upon the correct Google query and found the answer!!

Google toolbar highlights autofill fields

The link above will tell you how to turn that feature off. Personally, I don't use the Google toolbar because it seems an invasion of privacy and I don't think it's available for Linux, anyway. But it's a good thing to keep in mind how other internet programs can affect your browser.