Recently I started using Tmux, but I noticed that it causes a strange Emacs glitch. When I open source code for elisp or haskell, the comments aren't highlighted. Only the comment sign is (; in case of elisp, -- in case of haskell). The rest of the commented line is in normal colour. When I run Emacs outside of Tmux everything works as expected - the whole commented line is highlighted in a colour denoting a comment. Any ideas why this is happening?

SOLUTION: Based on Stefan's comment I added this to my .emacs file:

(custom-set-variables
 (custom-set-faces
  '(font-lock-comment-face ((((class color)
                              (min-colors 8)
                              (background dark))
                              (:foreground "red"))))))

Now the comments are displayed in red, just like comment delimiters.