Breakthrough bleeding is common with continous oral bc. Your doctor may tell you to have a few normal periods on the bc before doing continous to stop the breakthrough bleeding - your choice though. When on continous bc, the lining of your uterus is not supposed to shed. But it might kind of shed a little bit. Which can cause initial light spotting the first couple months of treatment. Part of the birth control keeps a nice mucus plug at your cervix, which can stop this blood from coming out. If the mucus plug comes out later (a couple months into treatment), you could have spotting too. It may be brown, almost black or dark red. That is 'old' blood. If you have light pink spotting often and post 2 months of treatment, you might want to get checked for cysts as that can be more common with lo loestrin. If doctor does suggest you have a period amd you do choose to have a period, it may be really dark/brown or have clots.