By Torah law, uterine bleeding renders a woman niddah only if it is one of four specific hues of red, or if it is black, and only if it is accompanied by a bodily sensation (hargashah). However, according to rabbinic decree, in order to prevent misjudgments, a woman becomes niddah as a result of bleeding of any hue of red, pink or black, and even if she feels no hargashah.
A woman usually becomes niddah through menstruation or other uterine bleeding. Bleeding that is caused by a wound, or whose source is not in the uterus, does not render the woman niddah. The bleeding from a wound is known as dam makkah, not dam niddah. When a procedure is done that is known to cause bleeding, a halachic assumption can be made that the bleeding is dam makkah. When the procedure is done during the seven clean days (especially, according to Ashkenazi tradition, when it is done during the first three of them) the burden of proof to make this assumption is greater.
Even if there is no evident bleeding, a medical procedure can render a woman a niddah. There is a halachic principle that the womb cannot open without any blood accompanying, even if not seen. There is, however, a minimum size of the opening that would make her a niddah. Thus it is important to ask the doctor the measure of the instrument that he inserted and whether he noticed any bleeding from the uterus prior to the procedure, and pass on this information to the rabbi to determine what its effect will be on the womans niddah status.
The biggest problem with a procedure done during the seven clean days is that one is still required to complete the necessary halachic internal examinations (bedikot). The hefsek taharah and moch procedure, as well as at least one examination of the first day of the seven clean days, should be completed prior to the procedure. While bleeding from the procedure or dripping of the brown dye/disinfectent during the procedure continues, one can skip the bedikot through day six IN THIS CIRCUMSTANCE. At least one bedikah mush be performed on the seventh day. If it looks as if you will not be able to do that examination without the cloth being stained, you should ask your rabbi how to proceed.