Fully marine sea snakes share a recent ancestor with terrestrial Australian snakes, yet the genomic changes that accompanied this land-sea transition are largely unknown. Our team has shown that some sea snakes have expanded “UV-blue” spectral sensitivity via adaptive changes to their short-wavelength-sensitive-opsin-1 (Current Biology 2020: doi.org/10.1016/j.cub.2020.04.061). Recent unpublished data now confirms that some sea snake species of the Hydrophis genus possess multiple SWS1 visual opsin genes. This suggests the potential occurrence of multiple visual opsin gene duplication events within the last ~15 million years of Hydrophis evolution. Gene duplications of this nature are of high evolutionary significance, as the advanced visual ability observed throughout much of the animal kingdom evolved via duplications of photopigment-encoding opsin genes and subsequent shifts in wavelength sensitivity of the copies. It is likely that this rare case of gene duplication has enabled sea snakes to shift from ancestrally dichromatic to trichromatic vision during their adaptation to marine life.