The other way to make color without pigment. A diffraction grating is a surface ruled with grooves finer than a wavelength of light. It cannot bend all colors the same amount, so it fans white light into its full spectrum by angle — a separate rainbow for each order. This is the sheen on a CD, on a beetle's ridged shell, on a peacock spider. No dye, no film: only spacing.
Drag left / right to tighten or loosen the ruling — the tighter the grooves, the wider the orders spread. Release and it drifts.