For a woman to become niddah as defined by the Torah, she must have a halachically defined sensation of menses, hargashah, immediately preceding her bleeding. A woman with a full fledged bloodflow is assumed to have had a hargashah. (Needing a pad may be an indicator of having a flow and not staining.)

Our sages decreed that stains without hargashah make a woman niddah. When they instituted this stringent decree, they incorporated certain grounds for leniency. These include stains being found on colored surfaces or on items that cannot contract ritual impurity. The practice of wearing colored underwear is based on these rabbinic caveats. Therefore, as long as you have no hargashah and the staining does not become a flow, you are not niddah, even if the stains' source is likely uterine and even if their color can be seen. (Further discussion of this topic can be found in our section on Stains.

When a woman has staining that does not render her niddah, we still advise her to abstain from relations for twenty-four hours, to be sure that a flow does not begin. If the twenty-four hours elapse without further staining, she is free to have relations. Please note that abstention in such a case, while advisable, is not required by halacha.

It is fairly common for women to have some irregular bleeding postpartum and while weaning as the body's hormonal environment changes. Independent of childbirth, mid-cycle staining commonly occurs as a result of estrogen levels dipping slightly at ovulation, thereby briefly weakening the uterine lining. There can be other causes of staining and any specific concerns are best brought to your physician.