I think they’re talking about the coloring in `git diff`, `git log --patch`, etc, which defaults to red/green for removed/added lines, respectively. (This can be changed with the `color.diff.*` config options, as seen in git-config(1).) This UI also provides an alternative indication, in the form of -/+ indicators in the left column, but the coloring does help a lot—presuming that you can see it.