G–ran,

> It does not check for 24 bits so the problem is not on the X side.
> The second question is why the VM is built like that, but that is Ians
> thing to answer - there is probably some logical explanation!

It just congealed that way.  I started with 8bpp PseudoColor only (my
machine at home was a Sun IPX at the time) and gradually integrated
support for higher bpps as and when they were sent to me (by people
with more expensive graphics cards ;).

Ian