Since I put in an IUD (Mona Lisa) I bleed (fresh blood) a little on the day I ovulate. If I wait another 7 days I will start to bleed again for real.
It would depend how much you are bleeding. If you are in a state of Tahara [not a nidda], you should be wearing colored undergarments. If there is small staining on colored garments this would not render you a nidda.
If you are in the middle of the seven clean days and wearing white garments, a stain more than about the size of a penny/shekel would be problematic. In extenuating circumstances, even during the seven clean days, one may wear colored garments or a sanitary pad which also have the leniency of colored garments.
If the bleeding is more than staining, and you are seeing/feeling a flow of blood this would require a new counting of seven days. If this is the case, consult with your doctor, sometimes readjustment of the IUD may help. Otherwise, if the problem persists, a different form of contraceptive should be explored.