You did tell us to keep an eye open for future sets. Well then, in your head, what are the colors of each main character (Tacenda, Highwater, Crunch, Willia)
Tacenda is GRW. The demons would be mono black, though Miss Highwater has some red and blue to her, while Crunchgnar has some red and green to him. Willia is White Green Black.
Is [Tacenda] still GRW at the end of novella, after picking up the entity?
I imagine that entity actually being green. A darker side of green, but still green. It evoked a feeling of destiny, and of putting it back together (which would be natural) and a kind of survival of the fittest attitude. You didn't get to see much of it, but this is my intention for it.
Think of the Entities as enormous mana reservoirs--the collected mana of a plane--that can be tapped to power spells, but with dangerous results. Davriel's Entity is pure black mana, while the entity of the bog is pure green. (Though in its shattered form, a lot of its instincts were about self-preservation, which comes across black in the story.)