Just recently during (probably my last) Sunray/VDI demo installation I ran into the problem that we could not get 24bit color depth on the virtualized Windows XPs.
The SunRay part of the installation (i.e. the Desktop Unit (DTU, aka. ThinClient) itself could not be the problem, because they always
are 24bit (incl their respective X session on the SunRay Server),
we also ran the RDP client (uttsc) with the -A 24 option to force it to 24bit (which it would default to anyway) ... but to no avail.
Of course as always
google is your friend; several people have posted and
blogged this already: under Windows XP you have to explicitely enable 24bit for RDP. So in the Windows XP image (or template) open the registry and change
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp\ColorDepth
to the value
4.
Not sure if you have to reboot the virtual machine (VM) then, but since rebooting a virtualized XP is quite fast anyway, just reboot it...