Dyes are certified, water soluble synthetic food colorants. They are manufactured as powders, granules and liquids. The synthetic dyes are of several types as per their basic compound and structure.
The Anionic dyes have a sulphonic or carboxilic group . The Catonic dyes have amino or aminomethyl as the basic group and are available as acid salts. Azo dyes have 1 to 3 azo bonds and make the largest permitted food dye. They have a primary aromatic amine and an aromatic compound and their combinations cover a wide range of colors.
These dyes absorb light and reflect certain wavelength that is perceived as its color. Dyes have to be certified for their safety to be used as a food or cosmetic colorant. A dye which is listed as "FD&C" is permitted by the Food & Drug Administration to be added to foods, drugs and cosmetics. "D&C" means the dye may be used only in drugs and cosmetics.