occasional magenta/green blotches

and maybe even a UV filter interesting. The Foveon does not capture RGB, but its own tri-set of color wavelengths. It may be possible some of those filters may help.

Also I still have some hope Sigma may be able to do something in SPP and depending how the RAW pipeline is in-camera and programability, maybe in a firmware upgrade.

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Raist3d/Ricardo (Photographer, software dev.)- I photograph black cats in coal mines at night...
“The further a society drifts from truth the more it will hate those who speak it.” - George Orwell