The face of LUCA (the last common ancestor) is unknown. The nature of this hypothetical primitive organism is actually a mystery. However, LUCA must had been drawn using a large number of colors in the painting about the origin of life.
In this talk, we will focus in one color: the blue. The blue color of a dye called as Prussian Blue. One will be reviewed its serendipitous discovery, its role in the work of great painters, its applications in several fields, its natural sources and, of course, its plausible role as prebiotic reactant to produce organic molecules in a likely scenario of the origin of life, which led to, in an unresolved way, the arise of LUCA.