What is a Pantone colour?

The value is in the standardisation rather than the inks themselves. Before it, matching a colour between two printers meant sending a physical sample and hoping. A Pantone number is an unambiguous reference: the recipe is published, so the same number produces the same ink in Lahore and in Hamburg.

The suffix on the number matters more than most people realise. The same pigment on coated stock and uncoated stock produces visibly different results, so Pantone publishes them separately — 286 C for coated, 286 U for uncoated. They are not interchangeable, and specifying the wrong one is a common cause of a colour that looks right on the proof and wrong on the finished job.

Colours are matched against physical swatch books rather than on screen, because a monitor cannot represent an ink. Swatch books also fade with age and light exposure, which is why they are replaced periodically rather than kept indefinitely.

Many Pantone colours have an approximate CMYK equivalent, and Pantone publishes those too. They are useful for jobs that cannot justify a fifth plate, but "approximate" is doing real work in that sentence: some convert closely, others noticeably less so, and the ones that convert badly are usually the vivid brand colours somebody chose precisely because they stand out.