AT LENGTH. :D
So, first off, I like Aquaman. I think Aquaman is a cool character who has maybe been underutilized and as a result under-appreciated. I was never one of those people who made jokes about how shitty and lame he was because he was from the sea and could communicate with sea life because I really thought he was cool and also those are really lazy jokes to make. He is King and superhero of the oceans which accounts for 75% of only the surface of the Earth, which is a hell of a lot of ground to cover.
However, I never have ever liked any costume Aquaman has ever worn. EVER. Granted, when he was first introduced he probably spent most of his time on land hanging out with Batman and Superman, but the costume doesn't make any sense for someone who comes from the ocean. Orange is a pretty terrible color if you're going for an ocean thing, and green would only look good if it was paired with blues. Regardless of what superspeed or superstrength Aquaman might have, he is still a slave to the laws of hydrodynamics. Scales on a fish are positioned so that the fish swims in one direction, forward. If Aquaman swims with his arms forward (as he is often depicted, probably to mimic Superman's flying) the scales on his shirt are now facing two different directions and would create drag. His gloves likewise serve no purpose other than to create drag, the fins on the cuff would do nothing because thats not how fins work. The fins on his legs are on his calves pointing backwards, fins are positioned like this on a fish because they move side to side to propel themselves, Aquaman does not. These are my main complaints.
Since there was nothing from the original design I cared to keep, I started from scratch.
First, physically, he needed to have the body of a swimmer so I gave him broad shoulders and a long lean torso. His hair was inspired by the Masked Bandit from the movie The Fall, I wanted to evoke a weird foreign look, but also something ahead of the curve and futuristic, something that might be the style in Atlantis. For his face I modeled him after the men in the paintings of JC Leyendecker, hunky handsome guys with thick necks and strong jaws. I wanted him to look like he is always smiling, so I gave him squinty smiley eyes and smirks, as a way to tie into the totally awesome fun-loving boisterous depiction in the Batman The Brave and The Bold cartoon. Since he comes from a people born to live in the sea, I gave him large hands and feet with which to swim. I also gave him gills on the sides of his chest, which are kind of hard to distinguish from his abdominal obliques. The reason they're on his chest rather than his neck is because if a person WERE to have gills, they would have to be pretty big to keep a person breathing, and they would probably be located with the existing respiratory organs.
Okay, onto his costume! Aquaman is the King of the sea but he is also its servant and protector, the king who marches into battle AHEAD of his armies, so he should have an air of regalia, but not excessively so. The basic shape I wanted to take from the bodysuits Olympic swimmers wear these days. I thought it would be silly to cover his gills with his suit so the cut of the top swoops in quite a bit. There's no realistic reason he would ever need shoes, even on land there is no boot that would be stronger than his own skin (shoes are pretty pointless for any hero with superstrength). The functionless fins on his high collar are there to look fancy and regal as are the two photophore tipped filaments on either shoulder. Rather than gloves I gave him decorative armguards made of orichalcum, a metal found only in Atlantis. They probably have intricate carving in them, but I didn't get around to showing it. The fins on his legs are on the outside of each leg creating a sort of dolphin fin look when he puts his feet together. I imagine him swimming around like a penguin or seal more than a human. For his "A" belt buckle, I went for a sort of shark tooth shape, but I guess it also looks like a fish tail on accident, which is okay!
The bioluminescent aspects of the suit seemed like a no brainer. Atlantis is at the BOTTOM of the ocean, light can't reach the bottom of the ocean, so obviously its dark down there. Aquaman has superpowered sight and stuff which helps HIM, but I doubt that all Atlanteans have such gifted vision.
I opted against giving him any weapons because I couldn't think of a good replacement for a trident, which I knew I didn't want to give him. Aquaman seems more sensitive to the plight of the common fish than, say, Poseidon.
In summary, tl;dr and I hope you like it.