Changing the diet can certainly cause changes in stool, even a week out. Their bodies may still be adjusting to the new program. It doesn't look concerning to me, you will be amazed at how much their feces can change color with the foods that they eat (if you ever feed watermelon, the droppings will be red, don't panic!). If it begins to be more watery or mucousy, you may want to have it checked out.