Design of optical imaging system for full-ocean-depth low-light colors

•Beam-splitting prism structure is proposed to solve energy attenuation problem, which is optimal solution to achieve the full-color imaging under deep-sea environment with large depth of field.•Optics design in seawater medium had been design specially, considering dispersion properties of the seawater, accomplish monochromatic aberration minimize.•The prototype has been produced and the experiment shows very high color reducibility of low-light performance in deep-sea environment.