The "dark" value actually applies to the `background` setting (which
I’ve omitted here since "dark" is its default value.)
I’ve given `color` the value "always", which will preserve colorization
when using `less` as a pager.
Extracted from `difft --help`¹:
Options:
...
--color <WHEN>
When to use color output.
[env: DFT_COLOR=]
[default: auto]
[possible values: always, auto, never]
--background <BACKGROUND>
Set the background brightness. Difftastic will prefer brighter colours on dark backgrounds.
[env: DFT_BACKGROUND=]
[default: dark]
[possible values: dark, light]
¹: which seems to be the authoritative source of documentation, as per
https://difftastic.wilfred.me.uk/usage.html#configuration-options
