Chemistry can seem like equal parts science and magic, but pH indicator strips are a little closer to magic. Just put a drop of solution on the strip and you'll be surprised by a sudden change in color. There are two types of pH test strips -- each carefully treated with chemicals -- to give you different information about acids and bases through color.
Litmus paper comes in two colors. Red litmus paper turns blue when exposed to a base. Blue litmus paper turns red in the presence of an acid. Litmus paper is of limited use since it only tells you whether you are dealing with an acid or base and gives no indication about strength.
Universal Indicator Paper
Universal indicator, or alkacid, paper is much more specific. It has a different color for every number on the pH scale. Red is the color of acids on alkacid indicators. Less acidic solutions are orange or yellow while neutral solutions are green. Basic solutions are blues and purples. Your indicator strips should come with a color chart to match shades to pH values.