Hi mama! At 4 months with mixed feeding, poop color can really vary, bonna babies usually have greenish or yellowish poops, which is totally normal, pero it can change depending on kung anong formula at kung gaano kalaki ang breastmilk sa diet niya. Since baby is active and happy, that's usually the best sign, pero if the color is something unusual like very pale, very dark, or may red/mucus, better check with your pedia just to be sure and get your peace of mind! Hang in there, poop anxiety is so real for us moms, lalo na FTM.