Ooh, setting my preferred scheme there worked - thanks! 
A bit weird that I could only set default dark mode there (Site settings âž” Basics), though - and only set default light mode in the theme settings. 
I’d consider adding a little note, preferably with a link, under where you set the light mode in your theme settings. Something like:
This sets the default light mode pallet for your theme. Click here to set default dark mode./Go to Site settings âž” Basics, to set default dark mode.
BTW., I’ve been having some fun with some transparecy and blur and your theme. 
(It gave me some z-index troubles, though - probably due to my noobness, which I’m still working out kinks with.) I especially liked how it gave the background swoosh some more weight!
Take a look if you want! (Still early days, though - as I assume you can see.)