Interesting. I have just started looking into a banding issue I was having when this thread pops up.
Using an Odroid C2 attached to a Panasonic Plasma. I also tried “disable auto colour depth switching” with no effect. Previously had an Intel system with LibreElec attached to the Plasma, with little banding noticed.
I have not tried switching output between YUV and RGB, but the video range discussion caught my eye.
Based on my understanding of the Amlogic HDMI driver, the dmesg echo (hdmitx) is showing the colour range that the HDMI connection is at (ie. transmit). GPU processing supposedly is “Auto”, but I never found a reference for that info. If the display negotiates as LIMITED, it outputs as Limited. Now, supposedly in the HK 3.14 kernel this is controllable, https://forum.odroid.com/viewtopic.php?f=135&t=26003 but broken (?). However in the CoreElec 3.14-Nougat Kernel, that routine is rewritten https://github.com/CoreELEC/linux-amlogic/blob/amlogic-3.14-nougat/drivers/amlogic/hdmi/hdmi_tx_20/hw/hdmi_tx_hw.c so I’m not sure if HDMITX_DWC_FC_AVICONF3 is controllable.
As for controlling the colour range within Kodi, the option was removed as it apparently didn’t work.
https://discourse.coreelec.org/t/rbg-full-and-limited-range-selection/2001/3. Would need to look back as to when this was reverted versus when the Kernel was switched to Nougat, as I suspect the HK Kernel bug is why the switch didn’t work.