If you wanted your diff output to be colored you have three options

  1. Use a verison control program that outputs colored diff output

    git diff --color=always old-file new-file | less -R
    
    note:Mercurial does not allow you to run its hg diff outside of a repository
  2. Use a text editor that allows for syntax highlighing of diff output.

    diff old-file new-file | vim -R -
    
    diff old-file new-file | joe -rdonly -
    
    note:When using joe you may have to manually set the syntax highlighting with ^T Y diff [return]
  3. Use a wrapper for diff called colordiff

    colordiff old-file new-file
    diff old-file new-file | colordiff
    
    note:that colordiff is just a wrapper and thus does not paginate adding a pipe to less -R would solve that issue