Nvidia consumer class cards (Geforce GTX) can only output 10 bit color in a Direct X11 exclusive fullscreen mode. To get 10 bit color output on the Desktop in a way professional applications use it you need a Quadro card and drivers. Nvidia is blocking this for Geforce cards, regardless of the control panel setting a Geforce card will not process/output proper 10 bit color output. Anyone in doubt just try this tool: http://www.necdisplay.com/documents/Software/NEC_10_bit_video_Windows_demo.zip
Works with my Quadro M5000, fails with my GTX1080. Same PC, a NEC SpectraView Reference 322UHD-2 as Monitor.
To test 10 bit output in DX11 exclusive fullscreen you can try this: http://forum.doom9.org/showthread.php?t=172128
Games that I know that can render in 10 bit with a Geforce card if your Monitor supports it:
GRID 2, GRID Autosport, Alien: Isolation. There may be more now.