I personally use the default theme. Unfortunately, I am also slightly colorblind (can still see most colors, but some shades can be difficult to “see”), which makes it a little difficult sometimes on my eyes to try to distinguish certain colors.
Personally, I find the code/code block colors (deep red) against the background (deep gray) difficult to read.
It would be a great feature to introduce various colorblind modes to simply tweak the default text colors to more discernable shades.