It turns out shell.el is deliberately doing this, as I expected. The regexps
they use for the matching are in shell-font-lock-keywords. They don't work
that well (e.g. matching "--whatever" in the middle of a line, but not at
the beginning) and I find the colors distracting, so I just disabled the
coloring with (setq shell-font-lock-keywords nil).

On Sun, Jan 16, 2011 at 6:11 PM, Steven Thomas <sthomas314@gmail.com> wrote:

> 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.
>