Cobalt Blue


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The spectral power distribution of light reflected by cobalt blue is in the purple region of the visible spectrum. [clarification needed] Purple is commonly defined[by whom?] as a mixture of blue and red colours. Cobalt blue strongly absorbs all wavelengths of light between blue and infra-red, and reflects wavelengths at the lower bound and at the upper bound of wavelengths human visual sensors can detect. [citation needed] The human visual system treats the visible spectrum as circular,[citation needed] in the range of approximately 400-700nm. Cobalt blue is therefore perceived as primarily blue but with a degree of purple. [citation needed] The degree of purple (as a percentage, reported by studies of color naming) is subject to individual variation. [citation needed] Individuals that are red-green colour blind (that is, who are red-weak) will not see the purple component and simply see cobalt blue as blue. A degree of red-weakness will vary the degree to which an individual perceives the purple component. [clarification needed] As the reflected wavelengths are at the periphery of human perception,[citation needed] the colour is perceived as quite pure (equivalent to a spectral colour). [citation needed] The sample shown by the spectral power distribution diagram has a dominant wavelength of 456nm with a saturation of 93. 8% (which means the sample measured is equivalent to a spectral colour which has been mixed with a small amount (6. 2%) of white light). Some digital cameras[which?] are insensitive to the peripheral wavelengths and as a result produce images that show cobalt blue as a dark blue. [citation needed]