The instrument used to measure the amount of chemical in a solution based on color is called a colorimeter or spectrophotometer.

Here's a breakdown:

* Colorimeter: A simpler instrument that measures the absorbance of light at a specific wavelength. It uses filters to isolate a specific color of light.

* Spectrophotometer: A more sophisticated instrument that can measure absorbance over a range of wavelengths. It uses a prism or grating to separate light into its component wavelengths.

Both instruments work by shining a beam of light through the solution and measuring the amount of light that passes through. The amount of light absorbed is directly proportional to the concentration of the chemical in the solution.

The colorimeter is often used in basic laboratory settings, while the spectrophotometer is used for more complex analyses and research.