Well, I guess I can start with the conclusion: I couldn't find enough facts online about the true history of black rice and what I presumed to be a treasured grain of Chinese Emperors.

Here is a fact of the origins of black rice, also known as purple rice or forbidden rice. It can refer to more than 20 varieties of Oryza sativa which carries a high antioxidant pigment of anthocyanin which is exactly what gives black rice its deep color.
Black rice is often called forbidden rice, supposedly because in Ancient China this black rice was specifically reserved for Emperors and the aristocracy. Consumption without approval resulted in death by hanging. It has a very low harvest yield compared to white rice of around 10 percent which adds to its rarity. With extremely healthy benefits this rice has been used for hundreds of years in traditional Chinese medicine and again adds to its allure. Not only is this rice cherished and praised in China where the majority of it is produced but other very common types can be found in Thailand, Indonesia, Philippines, India, Manipur, and Bangladesh all with their own sort of black rice.
Black rice is famous for its health benefits such as reducing inflammation, helping with allergies and improving the digestive system, beneficial for the heart and for diabetics, liver detoxification, protecting against high blood pressure, and fights cancer — you know, all the stuff a superfood does in a day. Yet there is a mention of avoiding consuming too much, as it can cause digestive problems.

I would be able to gather a vast amount of knowledge from black rice but the only proper reference I could find is U.K.S Kushwala’s 192-page research book on Black Rice which costs €85 for the ebook. That is something I am not willing to buy for that price.
Like NPR’s article on black rice or a site called Modern Farmer that calls it a “sinister black rice,” none of them have references… Finally, I stumbled on a site called Science Daily, but they only talk about how black rice became black. I want to know the history of black rice in China and Asia and can’t seem to find it, with further proof or references. Anyways, I found this kid on Reddit. He does admit his reference; which for some gut feeling I trust. So according to NegativeLogic and his comment from 4 years ago, here it is word for word:
I can't find anything in English or not behind an academic journal paywall, but I will do my best to explain.
First off, not to be rude, but if you think the idea of a special type of rice being reserved for the Emperor is hard to believe, then I think you really need to read (or watch good documentaries, or listen to podcasts) about ancient China.
Because if you find that hard to believe, you'll be in for some pretty big surprises.
The names for the rice in Chinese - Emperor's Rice; Fortune Rice tell you a lot. I'm not going to get into Chinese characters much, but suffice it to say the characters themselves directly connect it to the Emperor.
Black rice only yields about 10% of what white rice does. So it was prohibitively expensive - only the nobles could afford it, and the evidence suggests that earlier in Chinese history it was so exotic and rare that the Imperial household alone commanded the entire supply, because they couldn't get enough of it.
It shows up on tribute lists pretty regularly. Chinese medical journals make reference to it - for both longevity medicines (the Emperor's favourite hobby) and as an aphrodisiac (for the Emperor's other favourite hobby).
To be clear here - it's been available to those with the means to afford it for quite a while. Go back 500 years and any aristocrat could probably get some, it was just a matter of the cost.
You have to understand too that it's not a monolithic thing. Some Emperors probably demanded it be only for the Imperial household, other dynasties had different priorities and granted more or less freedom the aristocratic classes overall.
Punishment in ancient China basically operated off the belief that the punishment for the first offense should make it impossible for a second offence to occur, and so getting your hands on anything that was intended for Imperial use could be a capital offense.
Because the Emperor owned everyone in China, you could be executed for anything. Messing with the Imperial supply of luxury goods was probably not a smart move.
I doubt a lot of people were actually executed for stealing black rice, but it was certainly extremely valuable and I wouldn't be surprised if there was a black market in it.
Understand too that Imperial China lasted until 1911. There are people in China that know these things because Great-Grandma remembered the days when black rice used to get sent to the Imperial palace.
A lot of this is oral history, it's true - but it's far more recent than you'd think.
Source: I like food, I studied Chinese history in school, and I have spent too much time in China talking to people about food.
The fact that this person added his source at the end makes me believe this is credible. Do you agree?
I regretfully have been slacking on my posts, as cheesy as it sounds, I have a lot on my plate. Nonetheless, I am extremely grateful for the opportunity to write and continue nerding about food with you. I want to thank NegativeLogic and you, for taking the time to discover more about the history of food.
Fortune Ricely yours,
The Greasy Pen.