The Potion of Black Color tie-dyes Jack and everything he's wearing black. The weapon (or any other item) Jack is wielding is not affected.
Potion of Black Color is created by combining the reagents shown below in a Chemistry Lab. Note: If the third reagent slot is shown empty, this means that any reagent can be placed in that slot (You still need to have all three reagent slots filled to be able to create a potion).
Blue Coral (added in 2.4)
Quark Tupa (added in 2.3)
Quark Tupa + Orange Pitaya (Quark Tupa added in 2.3)
The duration of the Potion of Black Color is as follows: