Hi... welcome, and hope 'we' can help!
First of all: which version of the software are you running and what card are you using?
Also .. color depth is set through windows, if you really want to its possible but just do it in windows which will prevent some odd windows behavior (until reboot if it occurs)
Why are you trying to adjust color depth? Just curious .. there should be no need to do that these days.
But its there:
https://www.amd.com/en/resources/support-articles/faqs/DH3-008.html