I've just tested opening a specific video when my Ubuntu 18.04.1 LTS system does not have the amdgpu driver installed from AMD, and AFTER the driver is installed.
The video is fine when the default (Ubuntu provided) video driver is used. After the latest (18.50) AMD video driver (amdgpu) is installed (and computer is rebooted) this attached/linked video displays in bright colors.
See attached example screenshot of video issue.
If I add the following to the /etc/drirc, the issue disappears. The word is that this indicates there is an issue with rgb10 support (10 bit RGB or 10bpc ? )
<option name="allow_rgb10_configs" value="false"/>