Knockout removes underlying color information; overprint preserves it. These file settings are not the same as the physical order in which white and color are printed.
Process white is different from opaque white
A process-white object normally contains no ink. If overprinted, it may disappear rather than cover the artwork below. A dedicated spot separation mapped to opaque white ink is a different production instruction.
Why a single rule does not work
A workflow may place a named white spot above color in the artwork and control its physical position in the RIP. Another may generate white automatically. Do not apply a universal rule that all color must overprint white or all white must overprint color.
Check with the production workflow
- Confirm the required spot name and overprint or knockout setup.
- Inspect separations as well as the ordinary preview.
- Provide a reference showing which areas should be opaque or transparent.
- Do not globally change every overprint setting to fix one object.