Indigo can give clear blues that range from the tint of a pale sky to a deep navy that is almost black. It is derived from the beautiful indigo plant which has light purple flowers. The oldest known fabric dyed indigo dates back to 6,000 years ago. Indigo was used as a dye by the the Greeks and the Romans, who valued it as a luxury product. They named it after the origin of the plant – India. Because of its high value as a trading commodity, indigo was often referred to as blue gold.