The Forbes.com article Bacteria Become Art Tools In Annual Agar Art Competition says:
...People’s choice winner Zita Pöstényi, a microbiologist at SYNLAB Hungary Ltd, used three agar plates and four different bacteria to create a pattern inspired by Hungarian folk art.
Pöstényi used another trick to create her colorful plates. “I used a special media for this drawing,” she says, “It contains a chromogenic mixture which enables the detection of activities of specific enzymes.” Thanks to this special mixture, the four bacteria species she used all showed up in different colors, which allowed her to create the traditional folk art pattern.
Usually, these unique colors tells researchers something interesting about the bacteria, but for the ASM Agar Art competition, these colorful features have become the medium.
Question: How does a "chromogenic mixture" result in different bacteria showing up in different colors in such a vivid way?
American Society for Microbiology Agar Art 2019 Contest, People's Choice. "Hungarian Folk Art," Zita ... [+]ASM / ZITA PÖSTÉNYI