Colors don't appear right inside tmux

[nerdpad]

I previously thought this may be happening because my tmux didn't have TrueColor support enabled properly. I resolved my tmux TrueColor issue tmux/tmux#696, but my vim colors still do not match:

Relevant vimrc

if &term =~ '256color'
    " disable background color erase
    set t_ut=
endif

" enable 24 bit color support if supported
if (empty($TMUX) && has("termguicolors"))
    set termguicolors
endif

let g:onedark_termcolors=256
let g:onedark_terminal_italics=1

syntax on
set t_Co=256                  " Explicitly tell vim that the terminal supports 256 colors
set background=dark           " Enable dark background
colorscheme onedark           " Set the colorscheme

NeoVim Version

⇨ nvim --version
NVIM 0.1.7
Build type: RelWithDebInfo
Compilation: /usr/local/Homebrew/Library/Homebrew/shims/super/clang -Wconversion -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1 -DDISABLE_LOG -Wall -Wextra -pedantic -Wno-unused-parameter -Wstrict-prototypes -std=gnu99 -Wvla -fstack-protector-strong -fdiagnostics-color=auto -DINCLUDE_GENERATED_DECLARATIONS -DHAVE_CONFIG_H -I/tmp/neovim-20161130-73384-ctpyvy/neovim-0.1.7/build/config -I/tmp/neovim-20161130-73384-ctpyvy/neovim-0.1.7/src -I/usr/local/include -I/usr/local/include -I/usr/local/include -I/usr/local/include -I/usr/local/include -I/usr/local/opt/gettext/include -I/usr/include -I/usr/include -I/tmp/neovim-20161130-73384-ctpyvy/neovim-0.1.7/build/src/nvim/auto -I/tmp/neovim-20161130-73384-ctpyvy/neovim-0.1.7/build/include
Compiled by user@77979797-mac.local

Optional features included (+) or not (-): +acl   +iconv    -jemalloc +tui
For differences from Vim, see :help vim-differences

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/usr/local/Cellar/neovim/0.1.7/share/nvim"

Screenshot

Left: iTerm > tmux > nvim
Right: iTerm > nvim

Noticeable Problems:

• Background color doesn't match. Background color of nvim running within tmux has a darker tone
• Normally all colors look more contrasted (colors on left eg: pink, red, etc. are darker inside tmux

[joshdick]

Your .vimrc contains this line:

if (empty($TMUX) && has("termguicolors"))

Does everything work if you change it to:

if (has("termguicolors"))

[nerdpad]

@joshdick OMG! Yes, that solved the issue.

But if you don't mind can you please tell me, when the termguicolors is supposed to be set?

[nerdpad]

It's okay, I think I understand now that set termguicolors was not being called inside tmux session.

Thank you for the help.

[joshdick]

You're welcome! Keep in mind that this config will cause problems if you use tmux on multiple machines where only SOME machines have true-color set up -- every machine where you use tmux needs to have true-color configured.