  Second, even when properly taken as an inversion of experiences, one might suppose that the “spectrum inversion” function corresponds to flipping the spectrum over. That is, using the traditional names for the spectral bands, one might suppose the function maps red to violet, orange to indigo, yellow to blue, green to green, blue to yellow, indigo to orange, and violet to red. However, this is not the usual sort of inversion scenario (red is not mapped to green, for example). Further, this function is not defined for all hues. Many hues—in particular, a large range of “extra-spectral” purples—are not found in the spectrum.