Problem

Vim colouring is broken when run in tmux. But works without tmux

Suggested solutions

Numerous pages show solution in adding editing the default-terminal vairable in the ~/.tmux.conf file. Most of those focus on one of screen-something, rxvt-something or tmux-something

Contribution to the entropy

None of the suggested solutions solved the problem in my particular case but the

set -g default-terminal "xterm"

One may also check available terminal settings by putting an invalid name and launching vim: it will list all available ones. In my case the fallback was ANSI which resulted in white on black which was way better than black on black before