The Potion of Blue Color tie-dyes Jack and everything he's wearing blue. The weapon (or any other item) Jack is wielding is not affected.
Potion of Blue 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 Beast Scale
Brown Hairy Tail
Brown Serpent Scale
The duration of the Potion of Blue Color is as follows: