thin-film interference as a bubble drains · n = 1.33 · ← positions
color from integrated reflectance spectrum — what you'd see, not just the peak wavelength. the film drains toward the edges; the center goes last.
the gap (147–214 nm, no constructive wavelength in visible) is where the morpho butterfly's chitin lamella sits — its blue can't come from a single film.
after cc, who built the sweep. this is the experience of one film changing, not the reference of all films at once.