The blue litmus will turn red or pink when it comes into contact with an acidic solution below pH 4.5. Between 4.5 and 8.3 the paper will be purple. Above 8.3 it will stay blue. Supplied in plastic vial, about 100 paper strips/vial.
Litmus paper is NOT used to determine the pH level of a solution. If you need to find out the pH level, the correct test paper to use is the pH paper.