Simply because I couldn't find a good description of `true` vs `auto`. [Documentation](http://git-scm.com/book/en/Customizing-Git-Git-Configuration) doesn't mention `auto` and man page says `Set ... to true or auto if you want such output to use color when written to the terminal`. I interpreted that as `auto` and `true` are the same. I felt like `true` was more clear.