Jangan worry lah! Dark green or blackish poo (especially kalau baru few days old) is totally normal, that's meconium, the first poo yang keluar sebab baby digest amniotic fluid in the womb. Kalau baby sudah few weeks and still dark green, bolehlah boleh jadi the milk transit time je, tapi better check dengan doctor sebab sometimes it can mean baby tak getting enough milk or ada tongue tie issue. A few of my mum friends noticed their babies poo colour changed depending on feeding patterns, so it's usually not the formula itself lah, but your pediatrician will know best what's going on with your little one!