Stains, flow, and veset

Some Sephardi halachic decisors are more lenient regarding stains on toilet paper, not even requiring a fifteen-second wait!

It is difficult to provide a precise definition of "light flow" versus "heavy staining".  Were you to see the blood exit your body, it would be a flow.  Otherwise, a light flow would be comparable to your lightest period.  More would be a flow.  Less could be defined as staining (absent a hargashah, a bedikah, or seeing the flow depart the body).

It is generally advisable to abstain from the onset of staining until it becomes clear either that a flow is beginning or that the staining has ended.

Also, if you find a stain on your body in an area where menstrual blood can reach (i.e. much of the lower part of the body or the hands), it could make you niddah, depending on its size and color.  The color of a stain on the body can be evaluated if you transfer the stain onto a cloth (by pressing the cloth to the body).  Whereas distinct stains on a garment are each treated independently with respect to size (i.e., does any one stain exceed the size limit?), distinct stains on the body are evaluated together, by their total area (i.e., does the aggregate size of these stains exceed the limit?).  For a review of the laws of stains, see our article on the topic. 

We do not generally base veset calculations on stains.  Still, stains that do not render you niddah could theoretically count as a veset haguf were you to have a menstrual flow follow them three times in a row (without ever having such staining without a subsequent flow).  However, assuming you wear colored underwear and are not looking for stains in the bathroom, it is unlikely that you would notice such stains three times in a row prior to menstrual flow.  In the unlikely event that you were to establish such a veset haguf, you would abstain at the interval after having the stains at which your menstrual flow would be expected.  For example, if you were to establish that you stain this way twenty-four hours before a flow, you would observe an onat veset twenty-four hours after the staining.

We hope this helps!  Please don't hesitate to write back.