Ink Sac

Ink sacs are the darkest primary color dye.

Squids
Squids drop 1–3 ink sacs upon death.

Fishing
Ink sacs can be obtained as a "junk" item from fishing.

Compound creation
Ink sacs can be created from its base elements, using the compound creator.

Trading
Wandering traders sell 3 ink sacs for an emerald.

Trading
Librarian villagers buy 5 ink sacs for an emerald as part of their third tier trade.

ID
In Bedrock Edition, ink sacs have the ID name  with data value 0.