There are a variety of chemicals that react with blood in order to create a change in color. Examples would be phenolphthalein, o-tolidine, tetramethyl benzidine, and luminal. In some cases there are instances where blood is not visible to the naked eye so by using specific chemicals it helps to enhance the blood samples. The techniques used for enhancing the blood sample just depends you can either apply the chemical directly to the specimen, or by a transfer technique. The color that appears once the chemicals have been added tends to be a bluish color, unless there is some other specimen type present with the
