Yeah, it does leave a residue but I also saw bits of the photo layer degrading like a burnt out LCD pixel. Maybe it reacts but not corrode.
Shouldn't it be a green gel to deflect green out? Like chlorophyll.
The color of a filter is deceptive. The color can be the transmitted color reflected back from outside the filter, or it can be light reflected off the face of the filter. But, it is the color coming through the filter that is the important one. This filter definitely looks green, and I think it is light that passed through the filter twice that gives it that color. Another guess: it is to adjust the peak transmission into the green band, the peak at 550 nm shown on that little chart. It might even come closer to a PAR characteristic with no filter at all.