When LA-CO Regular Flux is applied on copper pipe; it can eventually induce a slight green coloring on the pipe. To prevent the green color from appearing, simply wipe the joint after soldering. This will remove residue and make your copper joint look great. The green coloring is due to oxidation. LA-CO Regular Flux cleans copper so well that the copper oxidizes quickly in order to prevent corrosion. LA-CO Regular Flux is water soluble, and it will prevent flux pitting corrosion from occurring on the inside of the copper pipe.