Initial preview for color contrast misleading

[robfentress]

The preview presented to the user for color contrast issues is misleading, if no background color has been specified. For instance, if I have specified a light red as my foreground color, the error it throws assumes the default white background. However, in the initial preview (before clicking the U FIX IT button) the text is presented on the standard grey background of the panel. The U FIX IT preview correctly places the text on a white background, but the initial preview does not, and this may be confusing. I think they should both have the white background, when no background color has been specified.

[bagofarms]

Fixed in #186