There are some faults with litmus. The color is very dilute, sometimes it is very hard to see. It is useless for deterimining blood and other colored solutions. It is a biological substance which can get eaten in biological reactions. Bacteriologists sometimes add litmus powder to milk, sterilize it and then inoculate the litmus milk with a pure culture of an unknown bacteria.
Some bacteria produce acid and turn it blue.
Others produce alkaline and turn the litmus blue. Others destroy the litmus and the milk becomes white. As an added bonsus, some bacteria curdle the milk or cause other striking changes. Therefore, we need many different pH indicators. Red cabbage color is more intense than litmus, but it loses its color and will not last years in the laboratory.