How do I get black rice seed and keep the colour and quality pure?

Source black rice seed from a reliable place, such as agricultural universities, the state department in north eastern states, ICAR institutes, or an established black rice grower or FPO, and ask for a named pigmented variety rather than a random sample. To keep colour and quality pure, you must avoid mixing with ordinary paddy, so grow it in a separate plot or with isolation, harvest, thresh, dry and store it separately, and clean equipment between varieties, because even a small mix of white grain lowers the value of a specialty lot. Maintain your own clean seed each year from a true to type field. Buyers paying a premium will reject lots that are mixed or off colour. Confirm the right variety and seed source for your conditions with your KVK or state university.