testing pills with multiple chemical components

Hello, I have a question regarding the reagent testing kits that are available on your site. It has come to my attention that there may be a question on the ability for them to test for multiple chemical components existing in one pill. As I am sure we all know, most ecstasy sold on the street is never pure MDxx, but an amalgamation of multiple chemicals that produce different results based on which test is used to identify them.

Example: Let's say I use the Marquis Reagent to test a pill that I KNOW is made up of both MDMA and Methamphetamine. I also know that the reagent test should show a color change of purple/black for the MDMA and orange for the Meth. However, since all wavelengths of light are absorbed by combination of Marquis/MDMA (hence the black coloring) how would the wavelength corresponding to orange show the presence of Meth (seeing as how it has been absorbed by the MDMA reaction)?

The only possible solution I can think of is that you must pay close attention to the reaction times in order to tell this, assuming that each chemical has a different reaction time. Ie. An instant orange fading to black in 5-10 seconds would indicate that the pill is indeed an MDxx/Amp combination. If you could enlighten me on this subject, that would be greatly appreciated.

*Please note that this would work for all testing reagents, I only used marquis as an example here for ease of comprehension.