Color Index or CI names for colors standardise names so that the artist can be certain of true ingredients in a tube. It is legal for a manufacturer to give any name to any color or to use 2 names to sell the same pigment. Aurora Yellow for example is the same as Cadmium Yellow Mid, yet is surprising how many people will buy both. Since the use of CI names the artist is better informed. Every color is classified in the index by number preceded by the color type. PR for instance stands for pigment red, NR stands for natural red and so on. This is the key: PW = pigment white, PY = pigment yellow, PO = pigment orange, PR = pigment red, NR = natural red, PBr = pigment brown, PV = pigment violet, PG = pigment green, PB = pigment blue, PBk = pigment black. Over time you will become familiar with the names. Ultramarine can be called New Blue, Permanent Blue, French Blue etc, but it is always PB 29.