belstaff, is it very dark brown or just yellowy brown? how is breastfeeding going for you?
there are 2 things I have persoanlly seen cause a dark brown vomit in a very young baby.
first was when baby had swallowed meconium and a few days later vomited all this nasty brown stuff up (when i was in hospital having ds1).
secondly if you are having probs breastfeeding and perhaps have cracked nipples. baby may have ingested blood that could make vomit appear brown