A universal indicator is usually composed of water, 1-propanol, phenolphthalein, sodium hydroxide, methyl red, bromothymol blue, sodium bisulfite, and thymol blue. The colours that indicate the pH of a solution, after adding a universal indicator, are:
The colors from yellow to red indicate an acidic solution, colours blue to violet indicate an alkaline solution and a green colour indicates that a solution is neutral.
Wide-range pH test papers with distinct colours for each pH from 1 to 14 are also available. Colour matching charts are supplied with the specific test strips purchased.