Actually, iridescence the effect of a coloured object that changes colour when tilted. Some butterflies display this property for use in attracting others when courting.
Iridescence is caused by the structure of the molecules on the surface of the object and is not caused by dyes.
The surface is created with layers of molecules, and in each layer, there is some transmission and some reflection of light. With enough layers, near 100% reflection of sunlight can be managed at certain wavelengths.
When the object is tilted, or the light is shone at an angle, the distance between the layers is then increased, so a different wavelength of colour is reflected. The new colour will always be of a longer wavelength.
Try the Nokia 6110 or breasts of pigeons or spectacles with anti-reflection coatings (green to purple).

Ir`i*des"cent [L. iris, iridis, the rainbow: cf. F. iridescent.]

Having colors like the rainbow; exhibiting a play of changeable colors; nacreous; prismatic; as, iridescent glass.

 

© Webster 1913.

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