The new version I uploaded contains some improvements about your second point.
Previously, whenever black or gray colors appeared on the screen, the bulb just showed white (the yeelight bulb can't produce black light as you know). Now, if you have auto-brightness disabled, that's not a problem anymore (auto-brightness handled that well). Black or gray tones will translate to a lower brightness. For the other colors, whatever brightness you adjust manually will be applied.
The challenge is that because of the Yeelight API implementation, I can't simply turn the bulb off when black is detected. When the bulb turns off, music mode (the command I use for movie mode) shuts down, so the bulb can't turn on again easily. At the moment, lowering the brightness to the minimum is the better solution.
I am already thinking of a solution that would allow me to turn the bulb off completely, but it will take time, and hopefully doesn't hurt performance or causes lag. It will need testing. For now, I just wanted to quickly release this method so you could enjoy movie mode a bit more.