If one uses black underwear, the stain will not show on the underwear, however it may show in the groin (next to the underwear). Does that render one nidah?
Stains on the body, on the inner thigh or inside of the legs, can make a woman niddah if their combined area is larger than a gris (roughly, the area of an American dime or Israeli shekel).
Whereas we judge the size of each individual stain on a garment independently, on the body we assess the cumulative area of all stains. When the cumulative area of stains on the body is a gris or less, the stains do not make a woman niddah.
In evaluating the size of a single stain extending from the body and onto a colored undergarment (of any color, not only black), only the part of the stain that is on the body is taken into account.
When the size is larger than a gris, the color of the staining is decisive. A light brown with no hint of a reddish tint does not make a woman niddah. A red, pink, or black stain would, as would some other browns. If the niddah status of the color is unclear to her, a woman can transfer staining (to the extent possible) to a piece of toilet paper or white cloth, and have that color evaluated by a halachic authority. In contrast, the size is best evaluated by the woman observing the stain on her body.
For more information, please see our site's article on Stains. Please write back with any further questions.
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