Blue has historically been a difficult color to either naturally find dye for or to replicate artificially, only rivaled by purple dye, as thousands of Roman-era sea snails can attest (via Smithsonian Magazine). One of the few ancient cultures to truly create a blue pigment — not a rough approximation like violet — were the Ancient Egyptians, who used theirs in art and cosmetics. Medieval Europeans also produced blue paint from ground lapis, a stone whose rarity made blue an exceptionally expensive color in the continent’s art (via BBC).  

In Central America, the Mayans also broke this mold with their own blue dye. Where the previous examples were based on a variety of different minerals, the Mayans made their blue from indigo leaves and clay. According to New Scientist, the latter material preserved the dye for centuries in the constantly changing tropical weather. While Mayan blue has survived in its application as paint to this day, records exist of another less-permanent religious use. 

To the Mayans, blue human sacrifices meant rainfall

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