virtualbox.org

I'm running VB on a Win7 64bit host with an XP 32bit client on a dual monitor system, where the client gets one monitor in full screen mode 1920x1200, while the host remains on the other monitor and I have an application I want to run in the XP client that requires 16bit color.
Basically from start, throughout all previous versions of VB I've had problems with this, because every time I switch color to 16bit it automatically reduces the resolution to 1600x1200 and every time I switch the resoltion to 1920x1200 it automatically increases color to 32bit.
In the past, with older versions of VB I just had to switch back and forth 4 or 5 times and sooner or later it would take 1920x1200 @ 16bit, but now with the latest version this seems not to work anymore.
I've switched back and forth 100 times, no success.

Could anyone tell me how to solve this?

I can't answer your actual question.

However, what application in this day and age requires a 65536 color mode (a.k.a. 16bit color mode, hicolor mode)? That was a kludge that was only around for a few years in the 90s, during the transition from palette based graphics to full color (true color) graphics. The only reasons to prefer 16bit colors modes are the 33% memory saving, and the 33% memory bandwidth saving because you have less memory to shift. But in this day and age that just isn't a concern.

In any case, it's the Windows OS that has to support particular color modes. Applications don't usually care.

Are you sure that the application doesn't require 16bpp as a minimum, i.e. because it doesn't support palette based graphics? That would be a very different (and more credible) scenario.

Sorry for late answer, had some trouble with my hardware, ending up buying a new computer.

To answer your question:
If it weren't for those old programs, mostly games I wouldn't need a virtual PC.
I know there are users who see VirtualBox as a tool to test things without messing with the host system, but I use it exclusively to run way obsolete software.

In this specific case it's far worse than you imagine.
The game I'm tring to play checks upon start the screen resolution and unless that's something with 16 bit color, it starts in full screen mode, which changes the resolution to what the game prefers.
It's actually written in 16 bit, so even in WinXP it was already obsolete and in today Win7 64 bit it doesn't even run in compatibility mode anymore.
The game itself doesn't have any setting for screen size, but if it finds a 16 bit color setting, it starts in windowed mode, where I can freely drag the window to the size I want.

I wouldn't really mind full screen mode, but then, all the graphics in the game are 4:3, which looks quite funny if stretched to 16:9.
Of course I could always before starting the game change the resolution of the guest system, but then I find it far easier having a VM that has the settings right to run the game in windowed mode, where none of the other programs I've installed in that VM have a problem running in 16 bit color.

I could always before starting the game change the resolution of the guest system

I don't know how to solve your 16-bit problem, but I use a free tool called Display Changer from 12noon
http://12noon.com/?page_id=80 on my gaming PC to set things up just right for FSX. Might work for your needs.

I would doubt that such a tool is useful in a VM. If it succeeds in changing the guests video mode, performance will be poor because it doesn't match what the host is doing.