After Newton had explained a series of ordinary spectra and Goethe had pointed out its complementary
counterpart, Nussbaumer discovered a series of extraordinary spectra which are geometrically
identical and colourwise analogous to Newton’s and Goethe’s spectra. To understand the geometry and
colours of extraordinary spectra, the wavelength composition is explored with filters and
spectroscopic setups. Visualized in a dispersion diagram, the wavelength composition is interpreted
in terms of additive colour mixing. Finally, all spectra are simulated as the superposition of red,
green, and blue images that are shifted apart. This RGB approach makes it easy to understand the
complex relationship between wavelengths and colours.