[RijilV]

I keep on pestering folks who work at Apple to add color filters to the per-app accessibility options, who knows maybe there's someone there who'll read this. (Edit: there is an internal feature request already)

Since iOS of a couple of versions ago, you can trigger color filters on and off from shortcuts, and get a similar behaviour, but it isn't perfect and sometimes glitches. I do this so my photos app and a few others are in color, but the rest are in grey scale.