I think you are confused.
If you have 32bit color (8 bit per 3 channels > RGB=24 bit plus 8 bit alpha >> 32 bit color) you actually have True Color, True Color is 24bit or 32bit (24bit + 8 bit alpha).
Back in the days yu had the option in the old control panels to change to lower color depth options, but that was removed:
Today, there is no option to manually change color depth, check "Ronald_Intel (Intel)" post in this thread:
For more info about True Color, check these links: