> I think Tony's point (pathological corner case
though it is) is that
> a B&W CRT *can* display color with such a filtering device; 
Well, to drag out the full-on pedantry, I would say that a B&W CRT
can't display colour, but a device of which a B&W CRT forms part (eg, a
B&W CRT plus colour filters and such) may.
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