Obsidian even more minimalist
Karadigm is in the official Community themes. No need to download a zip - pick it straight from Obsidian:
Settings → Appearance → Themes → Manage.
red, green, blue
Nearly monochromatic
Background, text and borders in shades of grey. Colour appears only where it means something - so the note stays the main thing on screen.
Clean typography
Calm type, airy line spacing and headings without ornament. Long text reads itself, short text doesn’t look lost.
Unified checkboxes
24 task states in one style - in progress [/], question [?], idea [I], finance [S] - plus five circular progress indicators from [0] to [4].
More subtle callouts
Instead of solid coloured blocks, just a thin coloured stripe on the left. A callout still catches the eye, but doesn’t shout.
Three colours, or your own
With the Style Settings plugin you switch the accent to blue, green or red - or pick a shade entirely your own.