A colour printed with its own pre-mixed ink instead of being built from CMYK dots.
Spot inks can reach colours outside the process gamut (fluorescents, metallics, particular brand hues) and print as solid areas without a dot pattern. Each adds a printing plate and cost.
A spot-colour reference number specifies an ink, not a screen colour; its on-screen preview is an approximation.
A brand orange that CMYK cannot reach is printed as a spot colour on packaging.
It is the usual answer when a colour must be consistent across print runs or cannot be reached in process colour.
A spot colour is specified by a reference in a matching system and, for precise work, by a CIELAB target or a full reflectance curve for the ink on a stated paper. The printed solid is read with a spectrophotometer and compared with the target as a ΔE00. For contract proofs, ISO 12647-7 sets an optional limit of 2.5 ΔE00 for spot-colour solids, while the offset printing standard itself permits spot colours without fixing a tolerance, so the tolerance is whatever buyer and printer agree.
| Colour | CIELAB chroma | ΔE00 lost, coated (FOGRA51) | ΔE00 lost, uncoated (FOGRA52) |
|---|---|---|---|
| Jade #00a86b | 53.6 | 0.0 | 4.4 |
| Orange #ffa500 | 83.8 | 0.4 | 3.7 |
| Emerald Green #50c878 | 56.8 | 4.3 | 8.7 |
| Royal Blue #4169e1 | 69.0 | 8.5 | 12.2 |
| Turquoise #40e0d0 | 45.4 | 9.4 | 13.5 |
Jade is printable on coated paper (0.0 lost) and 4.4 ΔE00 short on uncoated. Turquoise is 9.4 out even on the better stock and 13.5 on the other: no combination of cyan, magenta, yellow and black reaches it. A brand colour that behaves like the Turquoise row is the case a separately mixed ink exists for, and one like the Jade row needs it only on uncoated stock.
How this was calculated: Each catalogue HEX value is clipped at constant lightness and hue to Colourwise's cusp-triangle model of the published characterisation data. These are screen colours tested against two offset conditions, not statements about any ink maker's range.
A spot colour is chosen for a logo that will mostly appear on websites and in office printing.
The colour that defines the brand cannot be shown on screen or built in CMYK, so every everyday use is an approximation. Starting from a colour that survives in sRGB and process, and adding a spot ink for packaging, gives more consistency.
A file containing spot colours is sent to a four-colour digital press.
The press converts each spot to its nearest process build using whatever table the software has, and results differ between printers. Agreeing the CMYK equivalent beforehand avoids a surprise.