Linux – 32-bit color in virtualbox

I installed Ubuntu 9.10 (using the old version because it's bundled with PHP 5.2.10 instead of 5.3.x, which is a requirement for me with the project I'm working on). However, I can't figure out how to change the color display to 32-bit. Yes, I know 32-bit is really 24-bit + 8-bit alpha or whatever, but either way, I can't find a way to change it in Ubuntu/Gnome.

Here's the error I get when booting Ubuntu through virtualbox:

"The virtual machine window is optimized to work in 32 bit color mode but the virtual display is currently set to 16 bit.

Please open the display properties of the guest OS and select a 32 bit mode, if it is available, for best possible performance of the virtual video subsystem."

My host OS is windows 7 with a 32-bit display. I've tried allocating more video memory to the Ubuntu host, but that doesn't seem to make a difference.

Also, searching for this on google yields absolutely nothing. Every post or topic on this is from 2008 and discusses xorg.conf files which, to my understanding, are no longer used.

This seems so elementary, yet requires a 2 year degree in linux administration to change. In windows, you just right click the background and bam, you're done.

Please help.