Learn the basics about the pH scale, universal indicator and litmus paper. Indicators tells if something is acidic, alkaline or neutral. Indicators are substances that show different colours when they are in acidic or alkaline conditions. Litmus paper is a simple indicator that tells us whether something is acid or alkali. Litmus is red in acids, and blue in alkalis. It comes as red litmus paper and blue litmus paper. Red litmus paper changes colour from red to blue under alkaline conditions, bu