This app follows the official guidance to assume that a non-zero Level implies turning the bulbs on, so it only sends on() commands to devices selected as additional switches. If you put the bulbs in as both RGB devices and switches to turn on, though, it doesn't look like I currently do any deduplication, so that would be a not-too-hacky workaround.
I can't promise it won't break at some point; I did have a branch in which I probed the "additional switches" for RGB and CT capabilities and included them in those sets if enabled. If I ever do that, though, just put a virtual switch in those fields and have it send an on() command when turned on.
Also, you could consider using [PRERELEASE] Virtual Prestaging to manage the CT of bulbs that are off. 
