If I put a snow layer on the glass would that change it, I have the afk fish farm underground, in a secret part of my base, trying to keep it and its goods hidden. I first tried leaves, but came to the same conclusion you guys did, that it didn't work.
If I put a snow layer on the glass would that change it,
Probably not, that sounds like it would work.
The Wiki lists snow as "Transparent".
So try it out, either run the farm for the same length of time with and without the snow and compare the results or do some manual fishing and time it, if you ever have to wait more than 50 seconds it would seem to not be working.'
(Unless you missed the bite, I'd suggest testing it by building a largish glass/snow roof over a pool of water so you can see the trails the fish leave on the way to the bobber.)