We are sorry to hear of your miscarriage.
It is fairly common for bleeding after a
miscarriage to last for a number of weeks, much like
bleeding after childbirth. Yellow spotting, however, does
not preclude a woman from beginning her
clean days. Yellows on
bedikah cloths or
undergarments do not interfere in any way with the clean days; even some shades of brown may be permissible on the
hefsek taharah that precedes the clean days.
Therefore, you may begin the process of becoming
tehorah immediately, and ignore any yellow stains. Should questions regarding stains or
bedikah cloths arise, please
consult a halachic authority rather than assume that your clean days have been invalidated.
We wish you a refuah sheleimah. Please let us know if we can be of further assistance.