Additional experiment: details the methods of the additional experiment. Figure S1 depicts the Y maze apperatus for choice assays. Figure S2 shows the reflectance spectra of stimuli used in the additional choice experiment. Figure S3 presents the results of the supplementary experiment. Table S1 denotes the approximate chromatic (unitless) and achromatic (Michelson) target/background contrast of model ‘colourful and ‘luminant’ stimuli from Additional experiment S1, as modelled according to the visual systems of D.melanogaster and M. domestica. (PDF 329 kb