The wings of butterflies and moths consist of a colorless translucent membrane covered by a layer of scales. Each scale is a flattened outgrowth of a single cell and is about \(100\,\mu m\) long and \(50 \,\mu m\) wide.
The scales overlap like roof tiles and completely cover the membrane, appearing as dust to the naked eve.
The iridescence in the winas is caused bv multiple slit interference. Sunlight contains a full range of light wavelenqths. Interference occurs when light hitting the wings interacts with light reflected off the wina.
By the above explanation, it is clear that the beautiful iridescent (like a rainbow) colors on the wings of a tropical or morpho butterfly are due to thin-film interference of light.