Highlight white.

A white layer that goes down only where the artwork already calls for white, so white areas print brighter than the colours around them. CADlink defines it against the underbase: underbase adds white under the entire bounds of the job, highlight adds white only where white data already exists, and a separate highlight strength lets it carry a different ink volume from the base. Shops confuse the two and switch on highlight to rescue dull colour, which it cannot do, because it lands only on white pixels. What it does change is ink use and feel. Run at full strength across a big white panel, it pushes more white into an area the underbase already covers, and the print comes back heavier and stiffer than the approved sample.