Many synthesized dyes were easier and less costly to produce and were superior in coloring properties when compared to naturally derived alternatives. Some synthetic food colorants are diazo dyes. Diazo dyes are prepared by coupling of a diazonium compound with a second aromatic hydrocarbons. The resulting compounds contain conjugated systems that efficiently absorb light in the visible parts of the spectrum, i. e. they are deeply colored. The attractiveness of the synthetic dyes is that their color, lipophilicity, and other attributes can be engineered by the design of the specific dyestuff. The color of the dyes can be controlled by selecting the number of azo-groups and various substituents. Yellow shades are often achieved by using acetoacetanilide. Red colors are often azo compounds. The pair indigo and indigo carmine exhibit the same blue color, but the former is soluble in lipids, and the latter is water-soluble because it has been fitted with sulfonate functional groups.