Color Quality Only Upto 32 Bit In X64 XP?

I just upgraded to x64 version from 32 bit XP. But to my disappointment, the display properties only show up to 32 bit. Where is the 64 bit option? Here is the hardware I have: I had thought that while playing games, wherever there would be unmixed colors, they would now be mixed properly, like steam coming in dark areas in a game, or too many colors not fading into each other properly. But looks like I would need to do with the 32 bit only I guess.