There is actually a way to set whatever option of the flag you want to use.
So, for "Force Dark Mode for Web Contents" it goes like this:
- Enabled:
--enable-features=WebContentsForceDark
- Enabled with simple HSL-based inversion:
--enable-features=WebContentsForceDark:inversion_method/hsl_based/image_behavior/none/text_lightness_threshold/256/background_lightness_threshold/0
- Enabled with simple CIELAB-based inversion:
--enable-features=WebContentsForceDark:inversion_method/cielab_based/image_behavior/none/text_lightness_threshold/256/background_lightness_threshold/0
- Enabled with simple RGB-based inversion:
--enable-features=WebContentsForceDark:inversion_method/rgb_based/image_behavior/none/text_lightness_threshold/256/background_lightness_threshold/0
- Enabled with selective image inversion:
--enable-features=WebContentsForceDark:inversion_method/cielab_based/image_behavior/selective/text_lightness_threshold/256/background_lightness_threshold/0
- Enabled with selective inversion of non-image elements:
--enable-features=WebContentsForceDark:inversion_method/cielab_based/image_behavior/none/text_lightness_threshold/150/background_lightness_threshold/205
- Enabled with selective inversion of everything:
--enable-features=WebContentsForceDark:inversion_method/cielab_based/image_behavior/selective/text_lightness_threshold/150/background_lightness_threshold/205
- Disabled:
--disable-features=WebContentsForceDark
This was tested on Chrome Stable: Version 89.0.4389.114 (Official Build) (64-bit) and on Chromium: Version 92.0.4480.0 (Developer Build) (64-bit)
After setting a flag, you can check it out if it is used by going to chrome://version/, in the "Command Line" field.