I set up a registration form using frontpage and some of the text boxs have a yellow background colour in the browser to indicate they need to be filled in looking at the code i can't distinguish what tag sets this.
Do you use the Google toolbar for Internet Explorer? If so, this is a feature which can be disabled in a visitor's browser which removes the yellow fields. Has nothing to do with what fields are required in your form, you can denote those with your own method.
If not, post back with a link to the page in question.