Indigo is a blue pigment extracted from a plant with the Latin name 'Indigofera tinctoria' and is distinctive enough to be one of the seven named colours of the rainbow.
     For centuries the oldest example of a piece of fabric dyed with indigo was a piece found in Egypt which has been dated at 2,400 BCE, although there is written evidence of its use in the Middle East nearly 500 years earlier. Now a team of archaeologists from the George Washington University (USA) have found fragments of material whilst excavating the floor of the Huaca Prieta Temple, which is part of a prehistoric settlement near the Pacific Ocean in the Chicama Valley in Peru.
     At first no attention was paid to the fragment as the material that it had been embedded in was masking its true colour. It was not until a sample had been sent to University College London (UK) that he indigo dye was discovered, using high-performance liquid chromatography. The sample was also dated at 4,200 BCE, predating the Egyptian fragment by 1,800 years.
     Jeffrey Splitstoser, from the George Washington University, is quoted as saying "The people of the Americas were making scientific and technological contributions as early as, and in this case, even earlier than people were in other parts of the world. We always leave them out. I think this finding just shows that that's a mistake".

Edited from LiveScience (14 Sept 2016)