I’ve been known to take a black panel and make it white by printing and affixing a paper overlay and clear plastic.
Granted, that’s easier to do satisfactorily than a mostly black with white letters overlay, or really any other color combination (if only slightly easier). In fact that’s one of the reasons I chose black letters on white in the first place. But a commercial copy service ought to be able to do an acceptable mostly-black job, I’d think.