Those would be called indicators , simply google them and you should find many. I'll leave some examples "bromophenol blue" "Methyl red" and "phenol red".
Have a wonderful day :) thanks for the points
Answer:
The exhaust system of the car is the excretory system that removes waste.
The gas in the car is the digestive system that provides the necessary energy.
Answer:
The answer is: Molecule and Organ system.
