Art Spectrum® Indigo Blue is a deep purple between blue and violet on the spectrum. Here it is based on a combination of Ultramarine and Prussian blue. The colour has been used since ancient times when both the ancient Greeks and the Romans sourced it from India where it was made from the plant Indigofera Tinctora . Its name in Greek, ινδικόν (or ‘Indikon’), simply means ‘dye’.

ASTM Approved Permanent Colours American Society for Testing and Materials, conforming to standard D4302-90.