Every pigment has a unique Color Index Name, consisting of two letters and some numbers. It's not a complex code, the two letters stand for the color family e.g. PR = red, PY = yellow, PB = blue, PG = green. This, plus the number, identifies a specific pigment. For example, PR108 is Cadmium Seleno-Sulfide (common name cadmium red), PY3 is Arylide Yellow (common name hansa yellow).
When you're faced with two colors from different manufacturers that look the similar but have different common names, check the pigment's color index number and you'll see whether they are made from the same pigment (or mixture of pigments), or not.
Sometimes the paint tube label will also have a number after the color index name, e.g. PY3 (11770). This is simply another way of identifying the pigment, its Color Index Number.
