I'm new to Android, so making a custom shortcut or script to do something like that is currently out of reach. According to a little research, there is a command (requires root) to toggle "Negative colors". I have tested it and it does work (even though it blocks the regular method from changing that setting until the device is restarted).
echo 1 > /sys/class/mdnie/mdnie/negative
What would be the most user-friendly application to make a shortcut to do that?
Or is there some other way to more quickly and easily toggle Settings > Accessibility > Negative colors?