Using version 3.0

I have change the background color us the survey to a dark turquoise there is also a background image for the survey using the same color. All questions are using a the color white for the font. If a user tries to skip a mandatory question the modal error box pop-ups up with a white background which makes the error invisible. How can I change the background color or the font color in the modal window only?

That depends on how specific the CSS rule for color: white is but something like this at the end of your custom.css file should work:

Thank you for the response. I assuming you telling me to change the custom.css in the theme I am using. Is there a way I can do this just in the survey using Theme Options?

Not as far as I know.