Ah, normal lang yan mama, especially pag mixed fed! One of my mum friends' baby had the same dark green poop when she switched formulas, kaya siguro yung Nan Optipro is making a difference sa color ng stool niya, bawat formula talaga may effect sa consistency at kulay. As long as baby is acting normal, gaining weight, and hindi siya uncomfortable o constipated, you're good! But if you notice it's watery, has mucus, or baby seems fussy or bloated, better check with your pedia para sigurado lang, especially kapag ganyan na ang kulay.