There was a
color vector display technology that didn't use a shadow
mask or phosphor dots, but it was very uncommon. It used two layers of
phosphor with different activation energies, and the high-voltage supply
was actually switched between two voltages. The lower voltage only
activated one phosphor, but the higer voltage activated both, so two
different colors were available. This was used in the DEC VR20 monitor,
of which few units were believed to have been sold.
I haev an HP1350 'graphics translator' here -- it's an HPIB input vector
display generator. The manual mentions an HP colour vector monitor for
this unit, which would appear to work as you described, alas I've never
seen one (I have the HP1311 monochrome monitor only). I cna dig out the
model number if anyone wants to look for one.
I have looked in the HP1350 manual, the monitor in question is the
HP1338. I can find no mention of it on the web at all, alas.
According to the HP1350 manual, it had a 2-bit colour selection input,
providing 3 colours (the 4th state repeated one of the other colours).
Said colours were red, yellow, and green. I have no idea how it worked,
whether it was a shaddowmask CRT (but if it was, why not also have blue?)
or one with difference energy phosphors.
-tony