Actually I use vimdiff as difftool and vimdiff with molokai colorscheme to get a nice highlighting as you describe in your question.

1- git config --global diff.tool vimdiff
2- in vim ":colo molokai"

* Molokai @ https://github.com/tomasr/molokai
* Possible auto colorscheme with ~/.vimrc:

if &diff
    set background=dark
    colorscheme molokai
endif