The part of a dye molecule responsible for its colour is called the

Explanation

A chromophore is an unsaturated group such as the azo linkage or a nitro group whose delocalised electrons absorb visible light, and the wavelength absorbed determines the colour seen. An auxochrome such as the hydroxyl or amino group deepens the colour and, more importantly, helps the dye bind to the fibre. A molecule needs both to be a useful dye.