Variation in the sensory physiologies of organisms can bias the receptions of signals, driving the direction of signal evolution. Sensory drive in the evolution of signals may be particularly important for organisms that confront trade–offs in signal design between the need for conspicuousness to allow effective transfer of information and the need for crypsis of the signal to unintended receivers. Several genera of orb–weaving spiders include conspicuous silk designs, stabilimenta, in the centre of their webs. Stabilimenta can be highly visible signals to predators, warning them of the presence of a noxious, sticky silk web. However, stabilimenta can also be used by prey as a signal in avoidance of webs, creating a trade–off in signal visibility. I argue that the derived spectral properties of stabilimentum silk have resulted in part from this conflict. The innate colour preferences of insects, their ability to learn colours, and the spectral properties of flowers all suggest that the reflectance spectra of stabilimenta renders them relatively cryptic to many insect prey, while maintaining their visibility to vertebrate predators.