Normally colour is derived from pigment. This makes it possible to colour clothes, foods, paint etc by simply adding various pigments to the underlying substance.
Iridescent colour does not result from pigment but from sub-micron structures that causes interference and diffraction of light. This is called structural colour.
It appears that the peacock’s, bright iridescent feathers may be covered in brown (melanin) pigment. The pigment appears to absorb background light and in doing so make the iridescent colour appear more vivid.
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