The kind of light that we see things in changes how we see those things. This reef tank is shot under actinic light, which not only “ will facilitate photosynthesis or stimulate light sensitive species,” but it changes how the corals look, as well. From liveaquaria.com:
The light spectrum, or Kelvin rating, of aquarium lighting will also alter the appearance of corals… For example, bulbs that emit light heavy in the actinic blue range bring out dazzling fluorescent colors not visible under full spectrum daylight bulbs. While different hobbyists prefer different combinations of light spectrums, a typical lighting system for a reef aquarium consists of 50% white light with a high Kelvin rating and 50% blue, actinic light.
It’s also a lovely video of reef life to boot!