I use a Harmony remote to control my ATV and could never figure out a way to use the colored buttons to control functions in Channels, there are no commands in the Harmony app that apply.
Until today!
I discovered than when I put my LG TV into CEC mode it sends the color button presses to the ATV over CEC.
So I custom programmed the Harmony to send LG commands for those buttons when the remote is set to ATV. I now have full control. I also discovered I could program, in channel numbers and direct enter channels from the remote instead of just scrolling.