Just received my Dahua NVR from Andy. Installed the HDD and booted up to a screen with purple and green vertical lines. I changed the HDMI cable and the issue remains.
Thanks. I tried a third cable after posting and still had the issue. I think it might be an issue with the video output on the board. When the NVR boots up and displays NVR on the screen there are no purple lines but once the grid for the camera display comes on the screen blinks and the lines show up.
Maybe try changing the HDMI output resolution of the (unspecified) NVR in case it's exceeding the capabilities of the (unspecified) device it's connected to.