The Potion of Brown Color tie-dyes Jack and everything he's wearing brown. The weapon (or any other item) Jack is wielding is not affected.
Potion of Brown 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).
Brown Petal (added in 2.4.4)
Ivory Bone (added in 2.2)
Sponge Coral (added in 2.4)
The duration of the Potion of Brown Color is as follows: