The ivory drift of 2000s white kitchens was chemistry, not cleaning. Specify around it once and whites stay honest.
The two culprits
Aging solvent-borne finishes amber intrinsically — sunlight accelerates but darkness does not prevent it (check inside a cupboard door). Separately, airborne grease films yellow any finish and wipe away with proper cleaning; real yellowing does not.
The diagnosis test
Clean one hidden patch thoroughly: if the tone evens out, it was film; if the cleaned patch matches the aged tone, the finish itself has ambered and only respray or replacement resets it.
The spec that stays white
Non-yellowing waterborne 2K systems — our default for whites and pastels — hold their tone under UV testing where solvent films drift. Ask any supplier the chemistry question before ordering a white kitchen; it is one sentence on a quote.