The color change for the results should be ONLY on the liquid. If only the sampler changes color - the test is negative.

Strength color reaction depends on the amount of material quantity. If you will pick up a lot of substance - the color reaction will be strong, in case of traces - the color reaction will be weak.

The color reaction in a positive results should be purple, but you can get a grean or blue-green reaction in case of Cociane/Crack results.