The change of stool color is normal and is a good sign baby is getting enough milk. (expressing-mama.com)
The lack of bile can also lead to changes in stool color, causing it to become gray, pale yellow or even clay colored. (fitnessandpower.com)
See your doctor if green stool (or another unusual stool color) is ongoing or if you have other symptoms, like fever, diarrhea, nausea, vomiting, or pain. (verywell.com)