Color matching additivity principle

Photosensitive drugs in topical formulations can also be stabilized according to the principle of spectral overlay. Because the risk of the absorption of additives through the skin is reduced compared to oral drugs, a larger choice of suitable UV absorbers and colorants is available. Particularly, sunblockers, which are commonly used in sun creams, offer a variety of different UV spectra, which can even be combined to match the spectrum of a drug. 

Color cannot be measured because it is perceived in the brain. However, it can be specified instrumen-tally using additive or subtractive mixing to produce a color that matches the object color. In the former, a match to most colors can be made by the additive mixing of light of the three primary colors. A measure of the intensity of the three primaries provides a specification of the color. Primary colors are defined such that none can be matched by mixtures of the other two. The principle of additive mixing is the basis of the common tristimulus and spectrophoto-metric methods of measurement. 

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