Mixing of several indicators into each other, such mixtures can be prepared that display different colors in mediums with different pH values. A mixture of such indicators is called universal indicator.
Example: Kolthoff is a universal indicator. It is a mixture of 5 different indicators called methyl red, α-naphthalene, thymolphthalein, phenolphthalein, bromothymol blue. This mixture exhibits particular color at particular pH.
This mixture is red color at pH = 4, orange color at ph = 5, yellow color at pH = 6, green yellow color at pH = 7, green color at pH = 8, blue green color at ph = 9, pH = 10 Blue displays violet color and red violet color at pH = 11. Universal indicator cannot be used for all reactions. It is used only in special circumstances for certain reactions.