What is HDMI output color depth spec

What is the maximum bits per color that the SOM can output to HDMI port? Is it 8,10,12?
Is this true color depth which means the number of unique color increases as the bit depth increase.

For Nano, I believe it is 8.Although TX1 TRM may specify more possibilities, our sw driver only support 8. More color depth feature may be implemented on TX2 or AGX Xavier.

You could try to adjust the depth as below link and see it 12 can work or not.
https://askubuntu.com/questions/1557/how-to-change-the-color-depth