So the driver by default sends RGB levels capped at 16 to 235 (intended for TVs) instead of 0 to 255, making blacks dark-grey and whites light-grey. I've observed the same issue with Intel drivers. I can manually set it to full range, but every time I update my nVidia graphics drivers it resets HDMI to limited range.
It seems to me that it was a huge mistake to make HDMI a common standard for PC to monitor connections whilst there was no robust method to auto-configure the RGB levels reliably. There must be millions of PCs connected to monitors with HDMI with the output range incorrectly set to limited, resulting in sub-optimal colour reproduction (and worse, it's probably not bad *enough* for them to realise there is an issue). Consumers should never have to fiddle with obscure setting such as these, which were never an issue on DVI or VGA.