It probably uses a marquis reagent, which could theoretically be made at home, as it is just a mixture of formaldehyde and sulfuric acid[0]. There are also websites[1] that have a key describing the colors that a number of substances produce on reaction with various reagents.

[0] https://en.wikipedia.org/wiki/Marquis_reagent

[1] https://dancesafe.org/testing-kit-instructions/