Rainbow

Splashery stretches a drumhead over this Splash's outline, twelve inches across, and finds the ways it can ring. Its lowest is 883.8 Hz, 7 cents sharp of A5. The next fifteen are its overtones, and each one draws its own figure: sand gathers on the lines that stay still.

Tap it to draw the rainbow again, color by color.

A rainbow appears when sunlight shines into falling raindrops. Each drop bends the light, splits it into its colors and bounces it back out, so you see a rainbow when the Sun is behind you and rain is in front. Its colors always go in the same order: red on the outside, then orange, yellow, green, blue and violet on the inside.

Tap it and the arc blinks away, then draws itself again color by color, red first, each band sweeping from one cloud to the other behind a bright little pen. Then sparkles burst from both clouds. Seen from a plane, a rainbow can be a whole circle.

Made in Splashery. Its code is MIT.

This link opens it in the Playground. To put it on your own page, add the element and one script tag. Every option.