Can a 2nd screen display 10 bit color?

I have a new iMac Pro that I've got an external display attached to. The display supports 10 bit color (it's an NEC PA242W). When attached to my old computer (a 2013 Mac Pro) via HDMI, I was definitely getting 10 bit output. It's easy to test this by using a gradient ramp, like the one on this page: https://imagescience.com.au/knowledge/10-bit-output-support

With my new iMac Pro, I've got the NEC display attached via an HDMI cable, using Apple's USB-C Digital AV Multiport Adapter. Unfortunately, with this setup, I am not getting 10 bit color.

Does anyone know if the iMac Pro will support 10 bit output via Thunderbolt 3? I'm wondering if I just need to buy a Thunderbolt 3-to-HDMI (or DisplayPort cable) and bypass Apple's adapter.

Thanks.