You can even use 24bit, as long as you have enough RAM on the card (is came in three versions 1,2 and 4 MB). The major downside is that it is only supported by it`s own RTG system. The software works a little bit different and asks you everytime you start a new programm for the first time if you want it to open on a Retinascreen, kinda like Modepro. Some Programms get along with that approach other refuse to work as they rely on CGX or P96 functions. Screenupdate speed is quite poor as the mainfunction of GFX-cards in that time was displaying big still pictures in lots of colors, like a ready rendered scene.
There are a few driver around that use the Retine Z2 natively, like a driver for the VLab that gives you a color preview screen on the Retina instead of the default grayscale.
Have a look at here
http://www.amiga-hardware.com/showhardware.cgi?HARDID=460
