Starting with version 1.1.0.16 build 1268, you can enable dark mode for the Windows 11 Folder Color Changer main interface even if dark mode is disabled in Windows. (The Open & Save dialogs will use the Windows setting).

On the Tools tab, click the Settings file link to open the Settings.ini file in your text editor.

Simply add the line ForceDarkMode=1 at the end of the file and save the file.