Green, keep an eye out for lumps if you're not going to express at all, because mastitis is a killer. If you get a hot, red lump and/or flu symptoms, then get yourself to a doctor.
If you're concerned about soy formula, the other option is the neocate-type prescription formulas which are completely broken down to base enzymes (or...er..something like that) and are suitable for babies with allergies (without dodgy hormones in soy)