HKS is a German color system, which was developed by the companies Horstmann-Steinberg, Kast + Ehinger and H. Schmincke and Co., hence the name: HKS. It is quite common in Germany, but plays nor role internationally and is increasingly driven by Pantone color as a global system to the brink.
HKS is available in four different color guides:
HKS K for coated paper
HKS N for uncoated paper
HKS Z for newsprint
HKS E for rotogravure
The original 88 colors were a few years ago expanded with the new HKS 3000+ color fan to 3520 colors that do not really have different colors as opposed to Pantone, but have more shades through overprinting the actual colors with black. By doing so, 39 shades per color are generated.
As a spot color inks are called, that do not belong to the CMYK color space, but are printed as a real color in an additional inking. The most important representatives are PANTONE, HKS and TOYO colors.
As a bright CMYK Red is produced by overprinting 100% Magenta and 100% Yellow inks, a spot color, such as PANTONE Warm Red is printed as a real color in its own inking unit, and therefore can achieve a higher color gamut than the mixed CMYK colors. Luminous colors like Pantone 811 or metallic colors like silver and gold can only be reproduced by spot colors.
The disadvantage of spot colors is in the higher costs. A booklet with a PANTONE spot color and colorful images has to be printed using 5 colors: CMYK plus PANTONE red. This requires 5 printing plates and a printing machine with 5 color stations. The advantage of higher color space is so often contrary to the disadvantage of the higher cost.
Spot colors can be reproduced very well in modern proofing systems. The color variations of the proofs of Proof.de are published here and mostly reflect the PANTONE and HKS Colors to be well within the achievable Proof.de Gamut.
Color variations of Pantone colors in the proof in Delta-E
Color variations of Pantone metallics colors in the proof in Delta-E