There are 3 main types of cumin seed available: amber, black and white.
The amber seeds closely resemble caraway, fennel and ajwain seeds, and are a light yellow brown in colour with ridges and oblong in shape. These are the most common variation used in cuisines.
White cumin seeds are similar to amber seeds, just a bit paler. You can substitute white and amber if you only have one type available.
The black seeds are really a very dark brown in colour, they are lighter and sweeter than the other cumin and work well in creamy foods, rice dishes and the more unusual spice blends of Northern India and Persia.
Black cumin seeds are often mistaken for nigella seeds, when in fact they are very different spices.
HEALTH BENEFITS OF CUMIN
The health benefits of cumin include digestion, piles, insomnia, respiratory disorders, asthma, bronchitis, common cold, lactation, anemia, skin disorders, boils, immunity, and cancer.
Digestion: Cumin is extremely good for digestion and related problems. Cumin is also Carminative i.e. relieves from you from gas troubles and thereby improves digestion and appetite. Due to its essential oils, magnesium and sodium content, it promotes digestion and also gives relief in stomach-ache when taken with hot water (like aqua ptycotis and mint).