all as described in How do I use vim as 'git log' editor? doesn\'t work for git show . I use often
git show HEAD ctrl+z ps PID TTY TIME CM
This worked for me:
git config --global pager.show "vim -c '%sm/\\e.\\{-}m//g' -c 'set ft=diff' +1 -"
Crazy vim args found here: https://stackoverflow.com/a/17015531/610634