3 yellow filters stacked, doesn't quiiiite darken the sky more than foliage, but it does get close! this is also an evening sky so a little more turquoise than a deep blue. i guess my dream for this look would be like. an industrial machine-vision longpass filter that blocks nearly all blue light. still neat though

there's a pun to be made about optical filter / cigarette filter probably but i'm too sick for that sort of joviality right now

photos taken with a hoya red 25A filter.
dramatic skies? yes. but i still need to do a LOTTA contrast editing to actually get it that dark. and in the process foliage gets lost to the darkness too.... a yellow filter would perhaps be perfect, mostly preserve red to green and cut off blue and violet. but yellow filters are quite weak, only like 1-2 stops difference at most. definitely not enough to darken a sky more than the land. but.... what if... hmmmmmm...
wratten #12, #15, or #16. all long-pass filters. meaning they drop light below 500nm, 510nm, 520nm respectively. they're quite weak yes but subtract blue and (almost) only blue... what if . i stacked like 3 of them? maybe 4? i dont think id have to worry about vignetting cuz crop sensor. there would probably be awful internal reflection hell unless the filters were coated. but.... could it lead to... the advent of the analog version of the revered CRUNCH style https://streak.club/p/52899/crunch-by-999999999 https://streak.club/p/53026/we-can-crunch-harder-by-999999999 ???? probably not! but it might look cool!