As a nation of warriors, there's little doubt that Aztec leaders often saw red. But thanks to one of their innovations, the Aztecs helped the rest of the world see it as well.
Prior to the Spanish conquest of the Aztecs in the early 16th century, the European world had never experienced fabric dyed a deep scarlet color. The best cloth that could be produced was dyed with a plant extract known as madder red, which produced a paler color than the Aztecs were making. Their secret ingredient? The cochineal beetle.
The cochineal is a tiny beetle that lives on prickly pear cacti. Fortunately for cloth-dyers, but maybe not so much for the beetles, about one-quarter of the bug's body consists of carminic acid, which is what produces the red dye. This means that 70,000 insects were needed for every pound of dye produced. Once the dye was discovered by the Spaniards, they immediately began exporting it home and doing their best to keep the source a secret. This made it a staple of their economy for 300 years. The dye was so expensive that it was used only for the red coats of officers in the British army (while the rank and file wore madder-dyed cloth). The rich red also contributed to the robes of Catholic cardinals [source: Mursell].
By the end of the 19th century, a synthetic replacement for cochineal had been found and the bug dust fell mostly out of favor -- but not necessarily out of flavor. Cochineal is still used today as a popular food dye. It is, after all, completely organic.