Finding the pH using Litmus Paper?

First, if the species can break down to ions, therefore ions are not solid (not precipitate.) NH4+ is a Bronsted-Lowry Acid, so when a pH paper is put in the solution containing these ions, the blue litmus paper will turn red. But K+ and Na+ are spectator ions, so the litmus paper will not change COLOR. If you one to find the pH, I have to know the conc. of these ions in solution.