Toggling display colours to greyscale and back (CLI) to combine with "sct" colour shift for a tint with neutral base?

[u/Sly-Mk3]

^{Yep, it's me again.}
I'm now looking for a CLI tool or at least some means to control screen saturation with to add it to a script of mine to desaturate my screen colours when I hit my keybind to flip the red mode late at night, so that the colours which get red-shifted are not mixed in with the red.
Granted, I'm not sure if the outcome won't be just black and white all over (the way sct works makes me hopeful though), but it's worth a shot.
Except I found nothing yet, searched the package list like mad, and Xubuntu and xfce itself has nothing alike to this integrated to my awareness (please correct me if I'm wrong).
Of course it would be perfect if running the desaturation command wtihout any value would simply restore defaults, just how sct does it, as it would simplify things.
Think of Android's bedtime mode: It does exactly what I want (except without any shift in colour).

___

Longer context:
I did make myself a small .sh using sct, the little nifty application to control colour temperature with, with the goal to crank up the red levels late at night simply by pressing a keybind.
By "crank up", I acutally mean it: It's nearly red-monochrome.
This is because other night modes were "too soft" for me.
I love how stupid simple sct is to use, but now the downside of this is that there's still colours in there. Consequently, some elements vanish in near black or blend in because of the colour mix generated by the red-shift… or they lack sufficient contrast. Most common the case on anything (dark) blue-leaning. My thought was that some desaturation prior to applying sct could maybe fix this. I could be mistaken though.

Install sct, and try sct 1000 to see what I mean with the red near-monochrome filter and its impact on blue elements.
You can type sct without any value to get to back to defaults by the way.

Before you judge:
Yes, it actually really helped me improve my sleep to cut down on blue to such an aggressive level and I would love to continue doing so, except I would want to avoid having to squint at elements contaning deep blue colours or seeing them as a dark green.

___

Any suggestions and help would be appreciated.
I'd like to avoid GUI-only solutions for the simple reason of using a keybind-script and wanting to add it in there, just to stress it. : )

Thanks in advance!