See Low colour saturation Vero 4k - #9 by tgrun
Try putting it in /etc/rc.local before exit 0, or before setting anything permanently:
- Boot up
- Run sudo systemctl stop mediacenter
- Type sudo -s
- Run
echo 1 > /sys/class/amhdmitx/amhdmitx0/output_rgbbefore playing anything - Run sudo systemctl start mediacenter