In this context, particular means picky. From Merriam-Webster:
a : concerned over or attentive to details : meticulous
a very particular gardener
b : nice in taste : fastidious
She's very particular about her clothes.
c : hard to please : exacting
never loses patience even with the most particular customers
Scrooge is saying that Marley is being attentive to a rather unimportant-seeming detail, because Marley corrected his tense.
The "to a shade" vs. "for a shade" bit is a play on two different meanings of "shade."
In "You're particular, for a shade," the implication is that Marley is very picky, compared to other ghosts. (Shade would mean ghost here, as you guessed.)
I can only make an educated guess what the meaning of "You're particular, to a shade" would be since there could be a couple of ways to read it. But I'd choose a meaning for shade here along these lines, again from Merriam-Webster:
a minute difference or variation : nuance
I would then read it to mean something like, "You're very particular, right down to being particular about tiny nuances in meaning."
It's possible that "to a shade" has an idiomatic meaning I'm unaware of, or that it did in Dickens's time, but I couldn't find information about one.