I'm just manually changing regions by clicking timeline.
To use midi chord input you need to use:
ReaTrak midi chord input to region chord player.zip (green Help button at bottom)
To set the region color use this script:
ReaTrak-instant-trak-creator-gui.zip

You can try if if you don't mind a challenge or just wait for PG to put a midi chord detection element in the Plugin Standalone (just like Biab Window>MIDI Chord Detection). It's just a proof of concept example. Just another example of using Reaper (that many complain about) to improve PG products.

[Linked Image - Only viewable when logged in]