git: color diff auto

setup

@@ -17,6 +17,7 @@ fi
 # diff
 git config --global diff.tool vimdiff
 git config --global difftool.vimdiff.cmd 'vim -R -f -d -c "wincmd l" -c '\''cd "$GIT_PREFIX"'\'' -c "set noro" "$LOCAL" "$REMOTE"'
+git config --global color.diff auto
 
 # aliases
 git config --global alias.branches "branch --all"