Every packaging printer knows the feeling: the images are excellent, the register is clean, the job is technically good, and the client is looking at the corporate blue on the front panel with a doubtful expression. That asymmetry is not irrational. It reflects how human vision works.
The eye compares flat areas, and forgives pictures
In a photographic image, the eye has no reference. It cannot know what that particular shade of sky was supposed to be, so a shift of one or two DeltaE passes unnoticed. In a large flat area of a known brand color, the eye has a stored reference and a clean edge to compare against. The same shift becomes visible, and next to a previous production run it becomes obvious.
This is why a single tolerance across a whole pack rarely survives contact with reality. A tolerance loose enough for the images is too loose for the flat brand area; a tolerance tight enough for the brand area is unnecessarily punishing everywhere else.
Why spot colors drift more, not less
There is a common assumption that a spot color, being a dedicated ink, should be more stable than a process build. In practice several factors work against it:
- Large solid areas draw ink heavily and unevenly across the ink zones, which makes the ink and water balance harder to hold
- A spot color is often printed at high density, where small changes in ink film thickness produce visible color change
- Substrate absorption affects a solid far more visibly than it affects a screened area
- Drying and set-off behaviour on heavy solids can change the measured value between the press and the pile
The result is that the element with the tightest tolerance is also the one with the most reasons to move during a run.
Tolerances that hold up in a contract
A workable specification separates what is being measured. In broad terms:
- Brand colors on flat areas: the tightest tolerance in the job, agreed explicitly with the brand owner and measured on a defined patch, not on the artwork itself
- Process solids: a moderate tolerance, since they anchor the overall appearance
- Pictorial content: the widest tolerance, judged on overall appearance rather than patch measurement
Two practical points matter more than the exact numbers. First, agree the measurement condition and the instrument, because a tolerance measured differently at each end of the supply chain is not a tolerance. Second, agree whether the tolerance applies to a single sheet or to the run as a whole, because those are very different commitments.
Background on the underlying metric: DeltaE tolerances explained.
Extended gamut changes the question
For converters running many brand colors, extended gamut printing reproduces most spot colors from a fixed set of inks rather than mixing a dedicated ink per job. It removes washup time and ink inventory, and makes short runs of many SKUs far more economic.
It also shifts where the color risk lives. The brand color is now a build from several inks, so its stability depends on the stability of every one of them. Extended gamut without tight process control moves the problem rather than solving it, which is why the converters who succeed with it are usually the ones who put the measurement discipline in place first.
Holding the color once the press is running
Reaching the brand color at makeready is a solved problem for a competent operator with a good reference. Holding it for forty thousand sheets while the ink and water balance moves is the harder half, and it is where rejections come from.
This is the specific job of closed-loop color control: the sheet is measured continuously, the deviation on each ink zone is calculated, and the correction is applied to the ink keys while the press runs. On a heavy solid, where a small drift becomes visible quickly, the difference between correcting every few minutes and correcting continuously is the difference between a consistent pallet and a graded one.
The secondary benefit is the record. When a brand owner questions a delivery, a continuous measurement log of the actual run answers the question in minutes rather than defending it from memory.
Practical checklist before the next brand job
- Agree the reference, the measurement condition and the instrument in writing, before the job
- Set different tolerances for brand flats, process solids and pictorial content
- State whether the tolerance applies per sheet or across the run
- Confirm the press can hold the target automatically, rather than relying on interventions between sheets
- Keep the measurement record with the job, not in an operator's notebook
If you are not sure whether your press can hold a spot color automatically today, the free console check answers that from a few photographs, within one business day.