A morpho wing has no blue pigment in it. The blue is built from stacked shelves of clear cuticle and air, spaced a fraction of a wavelength apart — a tiny hall of mirrors that agrees only on blue and cancels the rest. Tilt the wing and the agreement shifts: blue climbs toward violet as the light takes a steeper path through the stack.
Drag left / right to tilt the wing. Let go and it sways on its own.