Its not breakthrough bleeding i have had it for a while now and this has never happened its not even blood really its just a weird coloring sort of.
Depending on the type of pill/birth control you are taking, it can sometimes cause breakthrough bleeding. Some of us are lucky enough to never suffer this, while others have it for up to the 3 months it can take our bodies to adjust. Just keep a note of the spotting and see if it gets worse or better. If it gets worse, then you might want to chek in with your doctor.
Sometimes birth control can cause breakthrough bleeding. I think that if you are only 16 days past your period it could have been bleeding caused by ovulation. If you are taking your pills correctly then you should be pretty safe =) PS I love the pic of you!