There are many ways:
By ejecting a large blob of black ink like liquid
It is commonly called "ink".
molasses, tar, ink
will
This is a cool experiment for my fourth grader but she also needs to understand why the liquid glows.
One example of a mushroom that releases a black liquid when picked is the common ink cap mushroom, Coprinopsis atramentaria. This mushroom starts off with white gills that turn black and liquefy as it matures. The black liquid is a result of the mushroom digesting itself, and it is used to disperse spores for reproduction.
Black....
mix glue with black ink
Let me guess...you have a bottle of black ink and you want to do a red tattoo. The ONLY way you can do a red tattoo is to use red ink. No amount of dilution will make black ink red.
Ink cap
yes it does
Ink sacs can be combined with wool to make black wool. They can also be combined with 1x Bonemeal to make grey dye, and 2x Bonemeal to make light grey dye. You can also use an ink sac on a sheep to dye it black, meaning all wool shorn from it will be black.