This is a human factors topic. OGS has two themes for the background: Day (bright white) can be unnecessarily harsh. Night is black but switching to a more typical window can be, to exaggerate, blinding.
It would be nice to have other options. For example, this OS has 10 stock solid color desktops. Of those, 3 shades of gray, and a sort of bluish-grey that look like good options. Maybe a couple other tinted greys, off-white, etc. would do. (vs. 250 possible stone/goban choices).
(A) The page should present users with a comfortable and suitable image to meet their visual needs (brightness, contrast, being able to distinguish display elements). Screen brightness and temperature can effect sleep cycle. (e.g., refer to https://justgetflux.com/research.html).
(B) When choosing color schemes it’s good to keep color blindness in mind. The topics (* and #) raises the issue of a visibility problem because changing to the Night theme results in insufficient contrast. Maybe the theme needs a tweak.
Some related topics: