Removing Background Image from Signup.php

So we're finally going to allow public users to set up websites through our website, and I go to open the signup page, and the page inherits the background from the theme. Normally posts in the theme have a white background, but on signup they don't, and the text color blends with the background image. Any suggestions on how to edit signup.php to fix this? Either CSS to give a white background, or to not load the background image?