Jadeblood Rainbow Drinker Theory

Jade blood is stated to be extremely rare in canon -- in fact, from what we know, it can be assumed that the only legitimate hue rarer than jade is fuschia itself. However, before the Empress exiled the adults from Alternia, as well as in Beforus, jadebloods had the task of tending to the Mother Grub and its children. It's been suggested that the Drinker trait was evolved to assist them in caring for the young -- and that could be correct, if we assume that jade blood is as rare as canon makes it out to be.

If jade blood is that rare, their natural midblood lifespans may have left the Mother Grub with spans of time without any attendants whatsoever. It may have, in order to protect itself, induced an undead state in its auxiliatrices -- so that when they died, they would simply rise up once more, ready to defend their queen.

(Tangent: What if the undead roaming the desert in present-day Alternia are actually the Jadebloods of history, long since driven to the point of madness and motivated only by their desire to feed? It's a common idea in vampire fiction that a vampire must war with their inner beast, their idlike desire to feast.)

After so long of that, it would simply be second nature for the Mother Grub to birth jadebloods with this quality, so that jadebloods are by necessity rainbow drinkers. A problem arises here: where are all the rainbow drinkers who appeared after the Empress exiled the adults from Alternia? The jade children from after this edict would not have been kept to the brooding caverns, as we see with Kanaya.

There are a few solutions to this.

#1: Jadebloods are only revived if they were killed in the process of defending others. Protection releases a chemical in trolls, perhaps also tying into moirailship; when this chemical is present in a jadeblood upon death, it induces an undead state.
#2: Something else must happen for jadebloods to become rainbow drinkers; all rainbow drinkers are jade, but not all jades are rainbow drinkers. Many have theorised that exposure to sunlight does it, but I don't buy that -- if jades were meant to stay underground in the caverns, they'd never get that trigger, and would not be drinkers in the first place. Others have suggested that Doc Scratch induced it -- but there were rainbow drinkers on Beforus as well, as shown by Porrim. Perhaps if the bodily fluids of another troll are injested shortly before/during/after death (we know, at least, that Karkat was crying when he tried to revive Kanaya), the process begins.
#3: All jadebloods -do- become rainbow drinkers, and the caste is so rare that it does not infringe heavily on the belief that drinkers are fictional.
#3b: All jadebloods -do- become rainbow drinkers, but they must feast on blood when they are initially changed, or they will die again, this time for realsies. In the beginning, this would have been to ensure that jadebloods kept to the caverns -- grubs are an easy source of blood which can't fight back, while the surface is full of adults who would have resisted long enough for the drinker in question to suffer -- while later on, it would have ensured that most jadebloods died for real when they carked it. Kanaya survived because of the multitude of newly-dead/mostly-dead bodies aronud her, which provided blood without resistance, much like grubs.

In essence, all jadebloods are born with the -ability- to become rainbow drinkers, and this ability was created in order for them to serve the Mother Grub more efficiently.

Fully-realised rainbow drinkers subsist off of blood -- but like dracula ants, they do not kill their victims. They are known to be incredibly fast, and may also enjoy increased strength, judging from Kanaya's effortless victory in the 3x Showdown. They are likely functionally immortal, being as they are no longer 'alive' in the technical sense, but probably have some form of achilles heel (much like Earth vampires).