Fig. 1. Colour stimuli and illumination sources. (A) Spectral irradiance of the UV+ (thin line) and UV–(bold line) illumination sources. (B) Spectral reflectance of a tomato plant flower (broken line), an artificial model flower (bold line) and the green foraging background (thin line). (C) Colour loci of stimuli in a colour hexagon assuming adaptation of the visual system to the green background colour in the UV+ and UV–illumination conditions. E, excitation; B, blue; G, green; UV, ultraviolet.