With color spot tests, a portion of an unknown powder/residue/crushed tablet is combined with a chemical reagent which may produce a color change. The color change is a presumptive indication of what the unknown could be. For example, the color test for cocaine is Cobalt Thiocyanate; addition of cocaine will produce a rapid blue color change. Another example of a color spot test is the Marquis test, which will produce a purple color with the addition of certain drugs such as Heroin.
