LP vs CD, much is also done in the recording and mastering process, modern mixing much more clean and clinical. Some CDs are not, you can hear noise (many recordings are still made with Valve desks, still can get noise with transistor desks too), fingers brushing against keys... etc.
I've seen it from lab prints from digital (laserjet to RA-4), print came back grey and dull.. though a case of no colour management at all.
"cream base" - many online hipsters colour cast their black and white levels in their images now so it's trendy.
As for remedies.. sunlight/UV will reduce the dyes, though it may start affect the denser stuff first? Sodium Hypochlorite rips everything off a film including dyes.. I'd suggest a weak diluted solution of laundry bleach.. but that'd start eating away at the top layers..
It sounds like you want some kind of reducing bleach. Metabisulphite + a small amount of sulphuric acid might be worth an experiment?