I wasn't actually expecting you to use an actual green filter in front of the lens when shooting this on b/w film

And that is exactly what I thought :D :D

did you pull down the greens in the channel mixer?

Let me think... Not the greens. But the blues to darken the sky. Then fixed exposure and added some shadows - this normally darkens all the wall stains.

edit: Red... was I messing with red? Maybe a little...