Everyone should be familiar with termguicolors, the option that allows terminal Vim to employ 24-bit color or true color. We use set termguicolors for vim to display RGB colors in our color scheme correctly.

However, true color may break if you are using Vim in tmux. If you have set up the tmux terminal properly, and Vim did not complain about not recognising your $TERM, you can try adding the following to your .vimrc:

let &t_8f = "\<Esc>[38;2;%lu;%lu;%lum"
let &t_8b = "\<Esc>[48;2;%lu;%lu;%lum"
set termguicolors

See xterm-true-color for explanation.