Colour detection is a technology used in counterfeit detectors to verify the authenticity of banknotes by analysing the printing inks used. Genuine banknotes are printed with specific and difficult to imitate inks that have a unique chemical composition. The detector uses an optical sensor to examine how these inks react to light, a process known as spectral colour analysis. In practice, this means that the sensor measures not just the visible hue, but the total spectrum of light that the ink reflects or absorbs. It then compares the data obtained with a database that stores accurate values for genuine banknotes. Counterfeits, which are often printed on conventional commercial printers, use inks with different compositions. The human eye may not notice this difference, but the detector's sensitive sensor can detect it because the spectral properties of ordinary inks differ from those of special inks. If the measured values do not match the reference data, the machine will evaluate the banknote as suspicious.