Barry Allen/The Flash
Barry's TV costume has a lot of similarities to the comics, but it's overall mostly been toned down. Instead of the smooth bright red, Barry's TV costume is ribbed and leathery. And while there are still lightning bolts on the costume, they're not quite as striking.
Oliver Queen/Green Arrow
Green Arrow has had lot of costumes in the comics, and his TV counterpart is no different. The biggest difference is that the most consistent element for Green Arrow in the comics is his pointy blonde Van Dyke beard, whereas in the TV show, it's the hood. The TV show has also toned down the overall palette and amped up the texture, just like with the Flash.
Dinah Laurel Lance/Black Canary
The classic Black Canary look in the comics features leather, fishnets, and a blonde wig. The TV show ditched the fishnets and added a domino mask.
Rip Hunter
Rip Hunter basically wears whatever the situation calls for in the comics, whether it's a t-shirt and jeans or a spacesuit. His TV counterpart pretty much always wears a cowboy duster.
Hawkgirl
Again, Hawkgirl's costume has been toned down and made much more leather-y. She still uses her classic mace in the TV show, although she doesn't have it until the end of the first Legends season.
Thea Queen/Speedy
Thea is sort of her own character, since Oliver Queen never had a sister in the comics. But she seems vaguely based on the second Speedy, Mia Dearden. Yes, that's an arrow-shaped boob window.
Roy Harper/Arsenal
Roy Harper has held many names in the comics — Speedy, Arsenal, and Red Arrow to name a few — but his basic characteristics are that he's a hot-headed ward of Oliver Queen. Again, he wears much brighter colors in the comics. Unlike Oliver, comic Roy rarely wears a hood.
Iris West
In the comics, Iris's family never adopted Barry. Also, she's a redhead.
Wally West/Kid Flash
Spoilers: In the comics, Wally had a tenure as both Kid Flash and the Flash. He's a redhead like Iris in the comics, where they're actually aunt and nephew instead of siblings.
Slade Wilson/Deathstroke
Slade's costume in the TV show is less colorful, and also avoids the fishscale effect. The character also doesn't have totally white hair like he does in the comics.
Firestorm
Firestorm has historically been the identity of many different characters. Jax is a character pretty much made for TV, although Ronnie and Stein exist in the comics. The costume looks far more metallic in the TV show. It's still pretty campy though.
Ray Palmer/The Atom
The Atom was initially supposed to be Blue Beetle, so it's no surprise that the TV show Atom is very different from the original. TV show Ray is basically Iron Man for a significant portion of Arrow, whereas in the comics his main power is shrinking, without a robot exoskeleton.
Hunter Zolomon/Zoom
Hunter Zolomon's story is pretty different in the comics. He used to be a good guy and instead of actually running really fast, he manipulates time. His comic costume is a riff on the original Reverse Flash costume, while in the TV show, they gave him an all-black Flash costume basically.
Captain Cold
A lot of Captain Cold's backstory is the same — he's a bank robber with a code and daddy issues. But his costume is way more campy and colorful in the comics. Also, he's traditionally drawn to be pretty ugly.
Floyd Lawton / Deadshot
TV Deadshot has never put on the mask he's most famous for in the comics. He usually just wears the eyepiece instead.
Ra's Al-Ghul
Ra's palette is much more muted in the show, and he doesn't have that goofy facial hair either. It's kinda similar to Oliver. Also, he appears to be of European decent, rather than Middle Eastern like he is in the comics.