Part of Orm's imprisonment involved placing him in a dry environment and rationing his water to rob him of his natural Atlantean strength. This reflects a weakness from the comics where Aquaman couldn't be out of the water for much more than an hour (this was adjusted to be more of a logical weakness over the years, and was eventually removed in 2011).
The visual effects crew invented new technology and VFX rigs for the underwater scenes in the film, with 100 cameras capturing the performances and action scenes and then applying them to 3D versions of the actors. This new setup came after James Wan found the rigs used on the first film to be complex and painful for the actors, and Wan wished to employ more versatile and safe equipment.
Orichalcum is Greek for "mountain copper", and is considered to have a traditional copper-red color, not like the green color it has in the film. But copper turns green when corroded by water or salt, which make up ocean water (that's how verdigris is formed). The color of corrosion also hints at how toxic it is.
Aquaman dons a blue stealth suit in this film, which carries the octopus-inspired ability to change color. The blue suit comes from the 1986 Aquaman comics.
The film's working title was "Necrus", the underwater kingdom in the Aquaman comics and seen in this film. Necrus is named after "necro", the Greek word for "dead".