--color[=<when>]::
Show colored diff.
- The value must be `always` (the default for `<when>`), `never`, or `auto`.
- The default value is `never`.
+ `--color` (i.e. without '=<when>') is the same as `--color=always`.
+ '<when>' can be one of `always`, `never`, or `auto`.
ifdef::git-diff[]
It can be changed by the `color.ui` and `color.diff`
configuration settings.