Azo dyes are man made. They contain the group -N=N-
Often this Azo group connects two aromatic groups--this makes a really stable molecule because the electrons from the N=N are drawn into the delocalised electron system. Azo dyes comprise many red, brown, black and yellow dyes as well as others. They are used for food colourings (including tartrazine), dying clothes (as the dyes don't break down in light/UV) and chemical indicators (like methyl orange, a pH indicator)
The building block for many Azo dyes is phenylamine, formed by the reduction of nitrobenzene by tin and concentrated hydrochloric acid.
+ 6[H] → …