A stain the size of a gris or smaller does not render a woman temei'ah, and neither does a stain on a surface that cannot receive tum'ah, such as a floor. Here is a third kind of surface on which a stain does not render a woman temei'ah: a colored one.

A colored surface

If a woman finds a bloodstain on a colored surface — colored underwear, a colored towel, or any other surface that is not white — the stain does not render her temei'ah.

Women often find this distinction between colored and white surfaces hard to accept. Why should a stain on one surface lead to seven clean days and immersion, while on another it changes nothing?

The usual answer is that the Sages decreed that stains on a white surface render a woman temei'ah but stains on a colored surface do not. True, but unsatisfying. Let us try to understand why they decreed as they did.

Rashi's explanation

One answer appears in Rashi, who explains that on a colored surface the color of the stain itself cannot be judged precisely.

An example from practice: when a rav or a yoetzet learns to examine bedikot, one of the techniques is to place the bedikah cloth on a sheet of white paper. That lets the eye judge the color on the cloth accurately. Hold the cloth against your hand instead and the color of the hand interferes: a beige shade on the cloth can read as pink against the reddish tones of the skin.

Rashi explains that when a stain is found on colored clothing, there is no way to assess whether its color is permitted. Since the exact color cannot be determined, the stain cannot render the woman temei'ah.

Hence the recommendation to wear color

Since stains on colored surfaces do not render a woman temei'ah, wearing colored underwear, using colored towels and sleeping on colored sheets are all strongly recommended. This is a recommendation, not an obligation. A woman who has no staining at all can disregard it.

Important: all of this concerns ordinary daily life. During the seven clean days the picture reverses, and a woman wears white underwear lechatchilah. A Sephardi woman may on her own initiative wear colored underwear if she has a problem with staining. An Ashkenazi woman with staining during the seven clean days may wear colored underwear only with halachic guidance.

When is it unclear whether a surface is "colored"?

Some cases are genuinely ambiguous:

In these cases a woman should ask her rav how he rules on such colors. Some rabbanim will want to see the color of the garment, since a verbal description is not enough.

Striped fabric — a modern question

Contemporary poskim disagree about striped fabric. The question is whether the white stripes combine with the colored parts of the garment.

An example: a woman wearing underwear with alternating pink and white stripes finds a bloodstain. Counting only the portions of the stain on the white stripes, it is smaller than a gris. Counting the whole area of the stain, it is larger.

Here too, a woman should ask her rav how he rules. If the color of the stain is unquestionably problematic, there is no need to show him the stain itself; presenting the question is enough.

Expanding the sources

Masechet Niddah (61b) records a machloket between Rabbi Natan bar Yosef and the Tanna Kamma regarding a stain on colored clothing, and the Rishonim divide along the same lines.

The Shulchan Aruch rules that a bloodstain on colored clothing does not render a woman temei'ah.

Disputes among later poskim

Rav Wosner rules stringently for a very light-colored garment, such as pale yellow. A family following Rav Wosner would need to ask if a bloodstain is found on a very light garment.

Darchei Taharah and many other poskim rule that even a very light color counts as a color, and a stain on it does not render a woman temei'ah.

Striped fabric — the sources