Lots of great suggestions, but I throw in my 2 cents: "dark" prog? Then VDGG Pawn Hearts is an absolute must along with much of their catalog. Universe Zero, Present, Art Zoyd are good recommendations already made but are in a different realm from mainstream prog rock (if there is such a thing) and in the realm of RIO/Chamber Rock with AZ mutating into minimalism/atmospheric electronics. But all great stuff that will expand your musical horizons.
... and speaking of RIO (rock in opposition) the place to start IMO is Henry Cow who I think are genius. You could start with the first, Legend which is more jazzy/Canterbury the next one Unrest which is darker and more avant, move on In Praise of Learning - a powerhouse that includes the great Dagmar Krause on vocals or the last Western Culture which is a dizzying instrumental tour de force.
Anyway you're in the right place - being exposed to new things and learning is the essence of becoming a prog snob, however admitting your ignorance is disqualifying!
<edit> you just got Scrotum Scissors take and since he's a walking encyclopedia of wonderful and arcane musical knowledge I'd go what that. But for Present I would start with Triskaidekaphobia - how can you not listen to an album whose title means "The fear of the number 13" if you are looking for dark prog?
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