PANTONE MATCHING SYSTEM (PMS) COLOURS / SPOT COLOURS:
Pantone colours are meant to be used for consistent logo design, as well as for bright and saturated colours which are difficult to produce from CMYK. This is especially true for purple, brown, violet and orange.
METALLIC OR FLUORESCENT COLOURS:
CMYK cannot produce colours that have metallic or fluorescent effect. If the design requires the use of metallic colour, spot colouring is the only option.
PROCESS COLOUR (CMYK):
CMYK is an abbreviation of Cyan, Magenta, Yellow, and Key (Black) is best for labels with pictures, photographs and produces a wide range of colours as it combines different percentages of each component to produce a whole range of colours.
Black is an addition to CMYK as they are unable to produce a proper black, so it is added to further enhance the blend.