The regular 8•24 card does provide 24-bit colour on my Hack IIx -- essentially a IIcx with more NuBus slots:



at least with System 7(.1), so it should do fine on the IIcx. Anyway, only up to 640x480 -- it will go up to 1152x870 but in 8-bit colour.

No experience with the 8•24GC, A/UX and very little with System 6, and that only on the SE/30.

Cheers,