Short answer
Because a render is light from a screen, while a pack is ink on a particular substrate, printed by a particular process, seen under shop light. Packaging multiplies the usual screen-to-print gap: one brand colour may be printed by offset on board, flexography on film and something else again on a can or label, each with a different gamut, and clear, metallic and brown substrates change colour before any ink lands.
A range of packs rarely shares one printing condition. A carton may be offset-printed on coated board, a pouch flexo-printed on plastic film, a label printed digitally, and a secondary case flexo-printed on brown corrugated board. Flexography — the dominant process for film and corrugated — meters fluid ink onto a raised relief plate and is associated with high dot gain, so tints print darker and fuller than on offset. Each combination of process, ink and substrate has its own achievable gamut. The same file therefore produces several slightly different brand colours unless the colour is defined as a measured target and each printer is asked to hit it within a tolerance. The general mechanics of screen-versus-print mismatch are covered on the print page; the packaging problem is that the mismatch happens many times over.
Process inks are largely transparent: they filter light that the substrate reflects. On white coated board that works as intended. On brown kraft board the substrate's own colour shows through, muting every colour and making clean whites impossible without an opaque white ink. On clear film the 'substrate' is whatever is behind it, so colour areas are normally backed with an opaque white underprint; on metallised film or metal, colour printed without white takes on a metallic, darker, angle-dependent look, which designers sometimes use deliberately. None of this is visible in a flat render, which assumes a perfect white surface.
A useful proof question: 'What is under this ink?' If the answer is not a bright white, the render is not a prediction.
Brand colours on packs are often printed as spot inks mixed to a target rather than built from cyan, magenta, yellow and black, because many saturated oranges, greens and blues fall outside a four-colour gamut. Spot colours cost press units and changeovers, which has driven extended-gamut printing — adding orange, green and violet to CMYK so that more brand colours can be built from a fixed ink set. Seven-colour conditions of this kind are now registered as characterisation data like standard CMYK ones. Either route needs the brand colour defined as a measured value on each substrate, not as a screen value or a swatch-book name alone.
Colour approval for packs is most reliable when it happens on a physical proof or press sheet on the production substrate, viewed under a standard viewing light, with measurements against the target. ISO 3664 describes standard viewing conditions for prints and proofs; measurement conditions for printed colour are defined in ISO 13655. A mock-up on a phone, or a render approved on a wide-gamut monitor, can promise colours the press cannot reach. Tolerances are normally stated as a colour difference (ΔE) from the target, and different substrates may need different targets to look like the same brand colour side by side.
Why: Different processes and substrates, each hitting a different reading of an on-screen value.
Fix: Define the colour as a measured target (CIELAB, with measurement condition) per substrate and set a ΔE tolerance for each printer.
Why: The brown substrate shows through transparent inks.
Fix: Use an opaque white base under key colours, or design a palette that works with the brown rather than against it.
Why: Approval on a wide-gamut screen of a colour outside the printing gamut.
Fix: Soft-proof against the actual printing condition before approval, and approve on a physical proof.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactModerate evidence
Flexography prints on plastic and metallic films, paper and corrugated board, uses fluid ink on a raised relief plate, and is associated with high dot gain.
Source: Flexography
FactStrong evidence
Extended-gamut printing conditions that add orange, green and violet to CMYK are registered with characterisation data in the same way as standard CMYK conditions.
Source: APTEC CMYKOGV Coated characterization data; CMYK Characterization Data (registry)
StandardStrong evidence
ISO 3664 specifies standard viewing conditions for judging prints and proofs, and ISO 13655 defines the spectral measurement conditions used for printed colour.
Caveat: Colourwise has read the catalogue records and public previews, not the full standards.
Source: ISO 3664:2025 Graphic technology and photography — Viewing conditions; ISO 13655:2017 Graphic technology — Spectral measurement and colorimetric computation for graphic arts images
Colourwise interpretationModerate evidence
Because process inks are largely transparent, colour printed on brown board, clear film or metal is changed by what lies beneath it, which is why opaque white underprinting is used where clean colour is needed on those substrates.
Based on: Follows from subtractive colour: transparent inks filter light reflected by the substrate, so a non-white substrate alters every colour printed on it. Colourwise could not locate a freely readable technical source on white underprinting practice to cite.
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.