I'm a sucker for stories that don't focus on humans, and I guess that's why black mould really hit the spot for me (and then didn't in the aforementioned bit where humans finally show up.) On that basis, I wouldn't compare it to "the colour out of space", but to Ligotti's "the red tower", or een Borges' "the library of babel." The closing of "the shadowy companion" is very telling of this, I think. And yeah, Mark Valentine wrote it, but it's very in tune with Mark Samuels. (Valentine says the story is based on a real meeting they had, so I'd like to think Samuels actually said something along those lines.
And I guess with all that's been going on here and out in the world I forgot to mention I got the book a while back and been slowly making my way through it but have very much enjoyed what I've read so far. Oops.