“…A color recognizer software was installed in the smartphone to quantitatively analyze the color changes of the sensors. The color recognizer offers 8 color modes: digital equipment corporation (DEC), hexadecimal (HEX), alpha-red-green-blue (ARGB), cyan-magenta-yellow-key (CMYK), CIELAB (Lab), hue-saturation-value (HSV), hue-saturation-lightness (HSL), and luma-chroma (YUV) 44 , 45 . After investigating the negative, weak positive, and positive results on three randomly-selected sensors (Supplementary Fig.…”