Ensure color consistency across different instances of 8-bit color windows?

I'm doing something wacky. Basically I have a bunch of VMs with Windows XP in 8-bit mode, and I want to take screenshots of the VMs running every so often. I would like the screenshots to be as consistent as possible, down to the pixel, so for example if the same app is running in two VMs, the app should have the same colors in both. However, it seems only Windows has direct access to the palette, and it seems that it sets it to whatever it feels is best, which could be different across d开发者_StackOverflowifferent instances of the VM... I've noticed that an app will have slightly different pixels if I change the background color of the VM, for example, but even on VMs with the same background color, they differ.

So, is there any way to set the palette as I want, or by some other means ensure these screenshots are consistent?

Good luck. I've tried comparing colors and pixels between two different test runs, on the SAME VM, and even that doesn't always match. (I was using TestComplete and trying to make an automated test to verify UI components matched.)