Image Courtesy of Alain Picard
Ordinary colour comes from normal chemicals that absorb some wavelengths of light and reflect others. An example of this is chlorophyll, which colours plants green. It soaks up the blue and red colours, but not the green, which is what you see when it bounces back to your eye.
Structural colour is where things get more interesting. This is dependent on the specific structure of the individual butterflies' wings. The colour can shift as the observer moves, an effect known as iridescence. You can also see this shimmery effect when looking through soap bubbles. It occurs when light passes through a transparent, muiltlayered surface and is reflected more than once. The multiple reflections intensify the colours. This gives butterflies their trademark glittery beauty.
8) Their wings are actually transparent