Final answer:
The medium that changes color to indicate bacterial growth is known as a differential medium, allowing distinction between types of bacteria based on color changes caused by their biochemical processes.
Step-by-step explanation:
A medium designed to change color to indicate growth of certain types of bacteria is considered a differential medium. These media allow researchers to distinguish between different types of bacteria based on distinct color changes that occur due to interactions of bacterial enzymes with substrates or by other biochemical reactions, including the lysis of red blood cells. A good example is the MacConkey agar, which turns hot pink when bacteria that ferment lactose produce acid, lowering the pH and causing the pH indicator in the medium to change color.