Gruvbox is a well designed, popular colorscheme for vim. This is a port to mutt and neomutt, in which vim can act as mail composer.
This is a replication of the repository here. The website gives further details and a screenshot, like this:
Download the files or clone the repo, e.g.
cd ~/.mutt
git clone https://git.sthu.org/repos/mutt-gruvbox.git gruvbox
Then source them in your ~/.mutt/muttrc, e.g.
source ~/.mutt/gruvbox/colors-gruvbox-shuber.muttrc
# For neomutt also add this line:
# source ~/.mutt/gruvbox/colors-gruvbox-shuber-extended.muttrc
The colorscheme is split into two files, where the latter also defines colors for neomutt.
GNU Lesser General Public License v3.