To test always use more than 1 reagent, because there are more substances than colors. Tests presumptively indicate PRESENCE, but not PURITY or QUANTITY. A positive or negative test result does not mean, that the substance is safe. No substance is 100% safe.
To identify other substances that could be present in a Methamphetamine sample, use reagents that with adulterants turn to a darker color than with Methamphetamine. Find all the reference information in instructions, color charts, videos & apps.