An apparatus including a treated tape, an adjustable color source, a photodiode, and a processor is provided. The adjustable color source emits a first radiation toward the treated tape and operates at each of a plurality of different target wavelengths in a spectrum. The photodiode measures a second radiation reflected from the treated tape, and the processor analyzes measurements from the photodiode to determine a peak wavelength from the plurality of target wavelengths. Based on the peak wavelength, the processor determines a color and darkness of a color stain on the treated tape. Based on the determined color and darkness of the color stain, the processor also determines a type and concentration of gas to which the treated tape is exposed.