Deep-sea fishes have evolved numerous morphological and physiological adaptations, including larger eyes or rod-only retinas, to counteract the low light conditions of their environment. Color vision in vertebrates is based on the expression of different visual genes (cone opsins) in the photopic cone receptors of the retina, while the scotopic rod receptors mostly expresses a single visual gene (rhodopsin) thought to mediate color blind vision under ‘dim-light’ conditions. Numerous duplications of the opsin genes in teleost fishes extended the molecular substrate for subsequent adaptation to variable light conditions. However, the molecular mechanisms of dim-light-only vision and the associated loss of color vision remains poorly understood. Here we report dynamics of opsin gene evolution based on 100 genomes spanning the teleost phylogeny, with emphasis on the deep-sea fish lineages. We found strong evidence for various cone opsin losses and pseudogenization in many of the deep-sea fish species, confirming the absence of conventional cone-opsin based color vision in these lineages. Interestingly, two deep-sea fish orders, which have lost most of their cone opsins, have consequently evolved up to 30 different rhodopsins with the potential to perceive various dim-light wavelengths. Thirty rhodopsin genes from one species show traces of strong adaptive evolution and we have further confirmed differences in the wavelength sensitivity by the opsin protein in-vitro expression. This strongly supports our findings of what might be the first evidence for rhodopsin-based color vision in vertebrates.