One interesting thing as a side-note is that after the filter first arrived I took a a snap as above, minus the eclipse and the histogram wasn't like anything I'd seen before:

I was expecting the peaks to be evenly spaced, I wondered if the filter and/or lens was doing anything funky but it does much up well with the Wikipedia "color vision" article that has a diagram showing human eye response:

Still the peaks seem to drop off more rapidly, I guess just a sensor limitation where the silicon / bayer filter response doesn't match the eye exactly? It looks pretty predictable so I thought that might have been the sort of thing that would be corrected, although that was a RAW import into lightroom so maybe it does happen during the display and/or export stages?