is this a theme problem?
 

hi i had a friend try and sign up to my community a while ago and they said they couldn't see what was being typed in the username and email fields.

i sent her a screenshot and she sent 1 back and i have know idea whats wrong as the fields look yellow? should be blue as in my screenshot.

link in my profile if you want to take a look

See how only certain fields are colored... To me it looks as though she has enabled one of the prefill form type options found with most browsers. If your text is light in color then that could pose a problem...