Rainbow Oil Sheen Swirling on a Wet Road Puddle

The colors in an oil slick don't come from the oil itself. Spread over a puddle, it forms a film only a few hundred billionths of a meter thick. Light bounces off both the top and the bottom of that film. The two reflections strengthen some colors and cancel others, depending on how thick the layer is at each spot, which is the same trick that colors a soap bubble. A raindrop has just landed in this oil slick jigsaw puzzle, set on wet asphalt by the curb with a few fallen leaves.