Thank you for reaching out to us.
We are sorry to hear of your miscarriage.
Staining on colored underwear does not make a woman niddah, nor does it interrupt the clean days.
Your status would thus ordinarily depend on the details of what you saw on toilet paper. However, in this specific case, you may attribute what you saw on the day of the ultrasound to irritation from the procedure and continue your clean days as planned.
If there was additional discharge later, it would be more difficult to attribute it to the procedure, because bleeding following miscarriage can come and go. However, it would still be subject to the usual leniencies of stains.
Please be in touch with any further questions. You also might find it helpful to read our article on pregnancy loss.
We wish you a refuah sheleimah!