Is Yellow Red? Hilchot Niddah and RGB vs RYB

MISHNA: There are five distinct colors of ritually impure blood in a woman: Red, and black, and like the bright color of the crocus [karkom] flower, and like water that inundates red earth, and like diluted wine. Beit Shammai say: Even blood like the water in which a fenugreek plant is soaked, and like the liquid that drips from roast meat, are ritually impure, and Beit Hillel deem blood of those colors ritually pure. With regard to blood that is green, Akavya ben Mahalalel deems it impure and the Rabbis deem it pure.

Rabbi Abbahu said in response: The verse states, with regard to a menstruating woman: “And she shall be purified from the source of her blood [dameha]” (Leviticus 12:7). The plural form of the word blood, dameha, indicates at least two types of blood. And another verse states: “And if a man shall lie with a woman having her sickness, and shall uncover her nakedness, he has made naked her source, and she has uncovered the source of her blood [dameha]; both of them shall be cut off from among their people” (Leviticus 20:18). The use of the plural form of blood once again indicates another two types, which means that there are four types of blood stated here.
The Gemara asks: But didn’t we learn in the mishna that there are five types of impure blood in a woman, whereas the verses indicate that there are only four? Rabbi Ḥanina says: The black blood mentioned in the mishna is actually red, but its color has faded, which is why it looks black. Therefore, although the mishna lists five kinds of blood, there are only four basic types.
This opinion, that black blood is actually red blood, is also taught in a baraita: The black color of blood that is impure is blood as black as ḥeret. If the black is deeper than that, the blood is ritually impure; if the black is lighter than that, even if it is still as dark as blue, the blood is ritually pure. And this black blood does not blacken from its outset, when it is inside the body; rather, it blackens only when it is removed from the body. This is comparable to the blood of a wound, which is initially red, but when it is removed from the body it blackens.
§ The mishna states that Beit Shammai say: Even blood like the water in which a fenugreek plant is soaked, and like the liquid that drips from roast meat, are ritually impure. The Gemara asks: But do Beit Shammai not accept the exposition of Rabbi Abbahu that the two mentions of the plural form of blood: “Dameha” (Leviticus 12:7), and “Dameha” (Leviticus 20:18), indicate that there are four types of blood here?
The Gemara answers: If you wish, say that Beit Shammaido not accept this opinion of Rabbi Abbahu, and they maintain that there are more than four types of blood in a woman. And if you wish, say instead that Beit Shammaido acceptRabbi Abbahu’s exposition, and the apparent contradiction can be resolved as follows: Didn’t Rabbi Ḥanina say with regard to the black blood mentioned in the mishna that it is not an additional type, as it is actually red but its color has faded? So too, with regard to the colors of blood mentioned by Beit Shammai, that of water in which a fenugreek plant is soaked, and that of the liquid that drips from roast meat, one can say that these are not additional types of blood. Rather, they too were initially red but their color faded.