Mrs. Sara Morozow gives a review of the halachos of Niddah and Hefsek Taharah.
*Note: Stains on garments are judged according to the leniency that applies to stains on a garment versus a bedikah, not because color is different on a garment.
**Note: Stains should be shown to a rav to determine status. If one has no access to a rav they may use the chart to determine size and then discuss this with their rav for a determination.