Starting to wonder if this is a bug with the theme or the way it’s set up by the author. So there’s two color palettes for Solarized Dark as you can see here:
The lowercase named palette is “not editable, owned by: solarized”. Unfortunately this palette takes priority in guest/incognito/logged out mode. The theme you directly edit is the capitalised colour palette above but that one only shows up after logged in.
Unless the author makes the original colours editable, I don’t think there’s much I can do here without hardcoding the css. Hope this makes sense, its’ tricky to explain without seeing it.
Edit: Hardcoding it overrode the un-editable theme color options in guest mode. I’ll just accept that as the solution for now.