one of `header` (the header text of the status message),
`added` or `updated` (files which are added but not committed),
`changed` (files which are changed but not added in the index),
- `untracked` (files which are not tracked by git), or
+ `untracked` (files which are not tracked by git),
+ `branch` (the current branch), or
`nobranch` (the color the 'no branch' warning is shown in, defaulting
to red). The values of these variables may be specified as in
color.branch.<slot>.