vim: do not use 24bit colors in tmux

.vimrc

@@ -28,8 +28,14 @@ set autoread
 set backspace=indent,eol,start
 set listchars=tab:>-,eol:$,trail:.,extends:#
 
+
 packadd! onedark.vim
 
+
+"Use 24-bit (true-color) mode in Vim/Neovim when outside tmux.
+"If you're using tmux version 2.2 or later, you can remove the outermost $TMUX check and use tmux's 24-bit color support
+"(see < http://sunaku.github.io/tmux-24bit-color.html#usage > for more information.)
+if (empty($TMUX))
   if (has("nvim"))
     "For Neovim 0.1.3 and 0.1.4 < https://github.com/neovim/neovim/pull/2198 >
     let $NVIM_TUI_ENABLE_TRUE_COLOR=1
@@ -42,8 +48,9 @@ if (has("termguicolors"))
     let &t_8f = "\<Esc>[38;2;%lu;%lu;%lum"
     let &t_8b = "\<Esc>[48;2;%lu;%lu;%lum"
   endif
+endif
 
 syntax on
-let g:onedark_termcolors=16
+" let g:onedark_termcolors=16
 let onedark_terminal_italics=1
 colorscheme onedark