I was having a similar issue with a Clevo N850HJ (although it was defaulting to green). There's no module in the linux kernel by default to deal with Clevo keyboard backlights, as I understand it.
I tried "clevo-xsm-wmi", and it worked. Don't know if it will work for the PS375sm, as the nearest mentioned on the link I provided is PS370SM-A, but it's worth a try.
(Note: this doesn't expose the leds in /sys/class/leds, but it does make the function key combinations work, and you can set options for the module it provides that set the initial state, so it can be coded to force the backlight off on boot)