The specular spectral reflectance (quantified in terms of reflection factor) from Calliphora vicina blow fly peaks at 437 ± 8 nm at normal incidence (a), corresponding to a blue visual appearance, as observed on a chromaticity diagram (b). With increasing incidence and viewing angles, the reflectance peak blue-shifts (a) giving rise to violet colourations (b). In addition, a narrowing of the peak FWHM is observed. Lucilia richardsi blow fly’s reflectance peak is located at 537 ± 6 nm at normal incidence (c), leading to a green colouration (d). With grazing incidence and observation angles, the reflectance peak narrows and blue-shifts (c) leading to blue and violet colours (d).