Tzovea (Coloring) - Breaking Down the 39 Melachot

Wrapping a wound with a bandage will  dye the bandage red, and cleaning up   a spill of grape juice with a paper towel  will dye the paper towel purple. However,   that is not an issue of the melacha of  Tzovea, which means dying or coloring,   because dying or coloring must be done in a  permanent and helpful fashion. And the bandage and   paper towel are not being improved by the stains,  and they're going to be discarded. And therefore,   there is no issue of Tzovea with bandaging a  wound and cleaning up a spill with a paper towel.