emerge --nocolor does disable color, but emerge --help does not give it as an option. I've made a patch for emergehelp.py, adding it to the option list and also adding a short description.
Created attachment 87024 [details, diff] Patch for emergehelp.py to show that portage does have a --nocolor option
Thanks, this is in svn r3377.
This has been release in 2.1_rc1-r4.