Even though the staining you describe occurs on a monthly basis, it does not render you niddah as long as it is only found on colored underwear, or on toilet paper (and you waited at least a few seconds after urinating before wiping). Unless you experience an actual flow of blood, such staining may be disregarded, and you may continue taking precautions against becoming niddah from this staining. We also advise abstaining from intercourse until the staining subsides and your status is fully clarified. (Stains larger than a gris on a white garment, or accumulating to that size on your skin, could make you niddah, depending on the color. Brown stains generally require evaluation by a halachic authority.)

Please feel free to get back to us with any further questions.