Colour depth is not related to OS or CPU.
Only monitor and video card determines it.
In Linux Mint 9, I was configuring a dual monitor setup, and discovered that Linux Mint only supports (at least in the Monitors app and the nVidia X Server Settings) 24-bit color depth. I am wondering if this is correct, because in Windows there is 32-bit, and this version of Linux Mint is 64-bit. I haven't used a 64-bit OS before, so please correct me if I'm wrong, could there even be a 64-bit depth? Probably not, but at least shouldn't there be a 32-bit option?
Acer P205H LCD monitor
Acer AL1706 CRT thin monitor
MSI PCIe 2.0 x16 8400GS-TD512H 512MB 8400GS