The colors indicating a positive drug test vary depending on which specific drug-testing tool is administered; therefore there is no standard one-stop chart for color decoding. Most at-home drug test should come with a color code, or have one available online.

Presumptive Tests

Some testing kits, like DrugCheck, offer only a positive or a negative result by showing one or two red lines, but come with color-coded strips pertaining to individual drugs. These colors do not correlate to those found in chemical reaction tests and are often labeled with the drugs name.

Pen Tests

Some tests, such as the Multi Drug Pen Ampoule Test MD-1, are used to detect traces of drug residue, rather than drugs used by a person. Often, the color-coding on these will correlate to the tests of urine, or other bodily fluids.

Specificity

Some tests are more specific than others, picking up anything from Advil to methamphetamines and may have a complicated system to distinguish between legal and illegal drugs. Others are broad, and more prone to error.

Range

In the pen test, colors are red and yellow based, while in the standard kit used by law enforcement, colors can spread over the entire spectrum from blues, to yellows, greens to reds.

Environment

Drug testing is not always accurate, and certain environmental factors such as temperature or humidity can affect the outcome of tests, even when they are presumptive and not color-coded.

Source:

DrugCheck

MediTests

National Institute of Justice