Artificial light at night (ALAN) is a globally pervasive sensory pollutant that disrupts biological processes across taxa and at all levels of organisation, but its impact on colour-guided processes remains largely unexplored. This is especially concerning given the rapid and ongoing transition away from narrow-spectrum lighting and towards broad-spectrum technologies like white LEDs, which are rich in the short wavelengths of light to which many taxa are especially sensitive. Camouflage is particularly likely to be disrupted by broader ALAN spectra, due to changes in the conspicuousness of background matching prey altering prey recognition in visually guided predators. We simulated natural intensities of moonlight with and without ALAN, using both broad-spectrum ALAN and ALAN filtered to remove the characteristic short wavelength peak of white LEDs to test how exposure to these light treatments impacted predator-prey interactions between the intertidal crab Carcinus maenas and contrasting morphs of the colour-polymorphic snail Littorina obtusata. Exposure to broad-spectrum ALAN reduced overall predation by more than half and reversed the pattern of colour-based prey selection observed under control conditions. Exposure to filtered ALAN removed any significant difference in attack likelihood between colour morphs. Our results demonstrate that spectral composition is a crucial aspect of ALAN as a sensory pollutant, capable of instigating profound changes in predator-prey interactions that could drive changes in population demography and increase morphological homogeneity in species that depend on colour polymorphism for camouflage.