Deb, did you use the DialogBox tag? If so, did you have that color something different from the site background? Where I'm having the main problem is that it's ignoring the DialogBox class tag. To have 4.8 be compatible, though I think I will probably end up changing all "class=DialogBox" distinctions in the .tpl files to add in bgcolor.
If only netscape coerced people to upgrade like microsoft does...