SimpleMind can show mind maps in Dark Mode.
The built-in style sheets support dark mode, meaning if you switch to dark mode the style sheet will as well.
For example, this is a mind map in Light Mode:
And this is the same mind map in Dark Mode:
Mac and iPad&iPhone: When your Mac is in Dark Mode, SimpleMind will be as well. You can change this via the main menu "SimpleMind"-"Preferences" or turn this off/on for stylesheets only by clicking the options wheel in Stylesheets.
Windows: Change to dark mode via the main menu "SimpleMind"-"Preferences". Or change the stylesheets only in Stylesheets, next click the options wheel and select Dark Mode.
Android: When Android is in Dark Mode, SimpleMind will be as well. You can turn this off/on for stylesheets via the options wheel above the stylesheets.