Normally, a six week old infant's bowel movements will be loose, yellowish to greenish, and not have a lot of odor to them. Very watery is a sign of diarrhea, and a harder, pebbly texture would suggest constipation. A breastfed infant will have what almost looks like yellow curdles in them.
They should be loose bowel movements but not too loose such as watery. Watery bowel movements suggest an your baby maybe sick with a cold etc. Mustard yellow to green in color is the average color of bowel movements. If your baby is breast fed than his/her bowel movements will actually look as if they are full of mustard seeds.
After the black tar period, usually they are mustard in color and consitency if breastfed. If formula fed they are darker and thicker, usually a stronger smell too.