Walnut kernel is priced on colour before anything else. The trade scale runs from extra light through light, light amber and amber to darker classifications, and the spread between the top and the middle of that range is large enough to dominate the economics of a contract.
The framework the trade writes against is the UNECE standard for walnut kernels, which sets out the colour classification alongside presentation forms, sizing and defect tolerances. It is a trade convention rather than Union law, and a contract that does not name the standard and the class has not invoked it.
Two practical points decide whether a colour clause works.
Colour must be judged against a physical reference under stated lighting. Perception under warehouse fluorescents and under daylight differ materially, and a dispute settled by two people looking at kernels on a table is settled arbitrarily. Both parties should hold a sealed reference set renewed each season.
Colour is not fixed. A light kernel darkens with age, heat and oxygen exposure. An extra light grade purchased honestly and then stored badly becomes a light amber kernel without anyone having done anything wrong. That makes colour a joint grading and storage parameter, and it is the reason a colour claim needs a defined measurement point in the contract – despatch or arrival – and a temperature ceiling to support it.
A related point often missed: darkening and oxidation are linked but not identical. A kernel can darken from heat exposure while remaining sensorially sound, and it can be rancid while still reading light. Colour grade and the oxidation panel answer different questions and both belong in the specification.
Hazelnut works differently. The commercial split there is natural, blanched and roasted, and within blanched the parameter that matters is residual skin, which shows as speckle in pale applications.