M-x shell, run 'emacs --help', get colorized output... why?

[Steven Thomas]

I notice that emacs shell-mode colorizes certain strings in the output of a command you run. For example most (though not all) words starting with - or -- get colorized. You can see this if you run emacs --help. I don't see this goofy colorization in term mode or eshell mode.

Can anyone explain what the deal is? A cursory look at the code in shell.el didn't reveal anything, but I'm sure that somewhere emacs must be deciding to add colors to the output.