I would have guessed no, but then I tried W97 with a bunch of schemes, 
including Marine (high color) and especially High Contrast Black.  :-)
Three caveats:
1.  Some scheme switches change widget sizes, which means we probably need 
to repack the frame widgets, too.  This gets fixed as soon as we resize, so 
it should be easy. 
2.  We're missing the necessary black-for-white swap when rendering the 
toolbar art against a black background.  Is this just a missing rebar 
setting, or will we have to reload the XPM?  
3.  I'm not sure what we'd use for a scheme-driven selection color.  I hope 
we can come up with something reasonable, because switching to XOR 
selections sucks.  
Or, if we decide to follow Web browser precedents and keep the document 
contents black on white, I wouldn't mind.  
Paul