Fig. 3.

Diagram showing how different optical properties determine a flower’s reflectance spectrum. In each panel only one optical property is varied to illustrate the different mechanisms; at the top of each panel three model petals are shown (illumination and observation are from above). (A) Changes in the amount of pigment will alter the modulation of the reflected light; little pigment yields a pale colour, and very much pigment yields a dull colour. (B) The intensity of the reflected light increases with the number of backscattering structures, which are illustrated by white ovals. When the reflectance increases, the transmittance will decrease. For the sake of simplicity, the relative modulation of the spectra was kept constant, although in real flowers the filtering by pigments will change with floral anatomy. (C) When the total amount of pigment remains constant but its localization changes, this will alter the modulation of the reflectance spectrum. Pigment deposition at the side of viewing yields the strongest modulation. For details, see van der Kooi et al. (2016a) and Stavenga and van der Kooi (2016).