Breast milk poop question....(not an actual photo)

So my baby has just started taking bottles of expressed milk at 12 weeks. She just turned 14 weeks today, so that’s 2 weeks of being at a babysitters with the bottles...I’ve noticed a change in her stool these last couple of days. It no longer looks mustard yellow and seedy...or even with streaks of green and mucus either...it now appears to be one runny texture that looks like the color palate below. I guess closer to the one on the right...I didn’t think of taking a picture of it today. Is this normal? I did catch the sitter heating a bottle in the microwave 🤦‍♀️ and I did ask her not to do it and tried to explain why (language barrier)...idk if she does this all the time and this is the result of her stools looking like this?!

Help 😩