There are many varieties of mustard, but three of the most known are the tiny blacks (Brassica nigra), brown (juncea Brassica) and the yellows of the white Brassica.
The Blacks and the brown ones warm up the physiology and distribute a pungent flavor to foods, according to ayurveda they balance Kapha and Vata, and they increase to Pitta dosha, they are considered very digestive and they alleviate to upset stomach as gases and the cramps. They are used much by all the Indian subcontinent where flame RAI, in Bengal comprises of a spice combination called panch puran and in the south the brown seeds in ghee or oil are fried to extract their flavor before adding it to soups, vegetable chutneys or plates. To the parrot that this process has its danger: when warming up the seeds (brown, black or yellow) and usually jump of the frying pan it is good idea to move the frying pan or to remove them to maintain them under control and to prevent burns. In a negligence a nothing funny jumped to me direct to the eye….
The yellow seeds (white Brassica) are less pungent than their dark premiums and much more used in the European kitchen, once ground form the base of the mustard. The flavor picantillo of the mustard comes from an essential oil that only forms when the worn out seed is mixed with water and it takes place above that it gives gives his characteristic flavor him to the mustard.
The yellow mustard seeds you will find them in stores of species whereas the brown blacks and only usually are on sale in Indian and Asian food stores.