1. One must be skilled at identifying colors of blood in order to rule on questions of Dam Nidah.
2. Rebbi Yanai told his children not to bury him in black or white shrouds.
3. Rebbi Chanina was expert at determining whether blood was Tahor or Tamei.
4. Rebbi Elazar once smelled a woman's blood and identified it as blood that came as a result of her desire for her husband (as opposed to menstrual blood).
5. Hashem enlightened Rava when Ifra Hurmiz tested him about the nature of blood.
A BIT MORE
1. Ameimar was able to distinguish between the color of the first tube and the second tube of blood taken from a person who let blood. Rav Ashi said about himself that since he could not tell the difference, he should not judge questions of Dam Nidah.
2. Rebbi Yanai reasoned that if he would be buried in black, he would merit being declared a righteous person, but he would look like a mourner among grooms. If he would be buried in white and not be deemed righteous, he would be like a groom among mourners.
3. Rebbi Yishmael cursed others who would use Rebbi Chanina's test for determining the nature of blood. Rebbi Yochanan said that he stopped ruling on blood because Rebbi Chanina used to contradict his rulings (based on Rebbi Chanina's expertise in blood).
4. The woman later confirmed that this was the case. Rebbi Ami remarked, "The secret of Hashem is to those who fear him."
5. Ifra Hurmiz sent Rava sixty types of blood to identify. He identified all except the last one. Hashem caused Rava to send her a comb, indicating (although this was not his actual intention) that he understood it was the blood of lice.