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The problem with editing the css for that page is, it might have undesired effects elsewhere.
If I were you, I would edit the template for that page (I think it's system_redirect.html - don't forget to clone the default template first, and use the cloned template as default). Find out the id or class of whatever it uses to set the colors, enter a new id or class to replace it in style.css, and change the id or class to the new one in your template.