Grep in Mac OS X's terminal -- only displaying one color

As Ignacio already said, OS X grep is a bit outdated (it's version 2.5.1). You can install the latest GNU grep though.

As always, you can install most missing Linux tools on OS X through Homebrew:

brew install grep

This will install ggrep so as not to override your existing grep. If you want to change that, see the info message:

All commands have been installed with the prefix "g". If you need to use these commands with their normal names, you can add a "gnubin" directory to your PATH from your bashrc like:

PATH="$(brew --prefix)/opt/grep/libexec/gnubin:$PATH"