adverb, adverb taking the 'to' particle, noun
Describes something that is intensely, vividly black. Often used with と or as an adverbial phrase to modify verbs like 光る, 輝く, or 染まる.
His hair shone deep black.
Jet-black clouds spread across the night sky.
Alternate spelling without the repetition mark; less common but still used.
Reduplication of 黒 (くろ, 'black') with the suffix 々, forming an adverb/noun that intensifies the meaning to 'deeply black'.