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On this theory colour is regarded as due to the presence of a “chromophore,” and dyeing power to an “auxochrome”; the latter by itself cannot produce colour or dyeing power, but it is only active in the presence of a chromophore, when it intensifies the colour and confers the property of dyeing.

Also the relative position of the auxochrome to the chromophore influences colour, the ortho-position being generally the most powerful.