Red litmus paper is dipped into a solution and stays red. Blue litmus paper is dipped into a solution and stays blue. Why did this happen?

Using Red Litmus Paper. Red litmus paper is dipped into a solution to establish whether a substance is acidic or alkaline. In an acidic or neutral solution, red litmus paper remains red ... When an alkaline compound dissolves in water, it produces hydroxide ions, which cause the solution to become alkaline.