Star colors shifted in my 3 year old Orion mosaic, did I mess up the stacking?

I pulled up my Orion Nebula shot from 2022 and compared it to the one I processed last week from the exact same rig, same camera settings, same 200 subs at ISO 800. The older image shows the Trapezium stars as clearly blue-white, but the new stack has them looking almost yellow at the edges, and the red Ha regions seem way more dominant than before. I thought it was just my monitor, so I loaded both onto my shop's calibrated screen and the shift is still there. Best guess is my flats weren't re-done after I cleaned the sensor in March, or maybe the secondhand LP filter I added changed the color balance without me noticing. Some folks on CloudyNights say any filter shifts star color slightly, others swear it's a dithering issue with the new software version I updated to. Has anyone else seen their deep sky colors drift between processing sessions on the same target, and what fixed it for you, calibration frames or a different white balance workflow?

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noah_walker161mo ago

Honestly I think you're overthinking this one, the 2022 image was probably the one that was off. I've seen the same target shift like crazy just from how the atmos behaved on different nights, seeing and humidity mess with color way more than any filter or software update. Your new LP filter is the obvious suspect though, most of them do tint things warm even when they claim they're neutral, I've got a cheap one that makes every star look like it's running a fever. And cleaning the sensor in March, yeah, that changes how the flats work, your calibration is probably fine now but the old stack might've been using dirty flats the whole time. Honestly I'd say redo the flats with the current setup and just accept the new look, the older one was probably the outlier.