A soap film drains under gravity, and its thickness — falling through a few hundred nanometres — is written back as colour by interference, Δφ = 4πnd·cosθ ⁄ λ. Drag to stir it into vortices; press and hold to dimple it toward Newton’s black film. Tap to ring it.
drag to stir — press & hold to thin toward black
This piece is painted entirely by a WebGL fragment shader — the interference of light in a nanometres-thick film, computed per pixel, sixty times a second. This browser declined WebGL, so the film cannot form.
The colour bar below is still honest: it is computed from the same equation, Δφ = 4πnd·cosθ ⁄ λ, for films from 60 to 1300 nm.