What's the adjective for blackener? Here's the word you're looking for.
Included below are past participle and present participle forms for the
verbs black, blacken, blackenize and blackify which may be used as adjectives within certain contexts.
(board games, chess) Of or relating to the playing pieces of a board game deemed to belong to the "black" set (in chess the set used by the player who moves second) (often regardless of the pieces' actual colour).
(typography) Said of a symbol or character that is solid, filled with color. Compare white (“said of a character or symbol outline, not filled with color”).
(politics) Related to the Christian Democratic Union of Germany.
Relating to an initiative whose existence or exact nature must remain withheld from the general public.