In the late 1960s, Marvel wanted to make sure it got control of the name "Captain Marvel" for trademark purposes, so Stan Lee and Gene Colan quickly came up with a character to go with the name. For the costume, creators had him wear a literal Kree captain's uniform, which in this case was a green and white outfit with a little flair to it. It was a decent enough costume for a rank and file character, but it was a weak design for a superhero. Unsurprisingly, the Captain Marvel series was a hard sell for Marvel. Marvel needed to keep it going, though, so the company brought in Roy Thomas and Gil Kane to revamp the series.
As noted earlier, patriotic-themed heroes were hot in the early 1940s. America was going through a strange period of both isolationism and nationalism at the same time. Americans were really proud of their country, but also didn't want to get involved in the war in Europe. Patriotic-themed heroes captured that feel, by having noble American heroes defeat villains who dared to come over here to mess with us. Things got bolder, though, when Timely Comics introduced Captain America, who broke out of the isolationist viewpoints by having the lead character punch out Adolf Hitler on the cover of the first issue, a full year before the United States actually went to war with Nazi Germany!
superhero costume kids
That said, like some other cliches, the sashes kept being used because they really do work. When Chris Claremont and Dave Cockrum took over X-Men, one of their goals was to revamp Marvel Girl, Jean Grey, and make her a bigger character. One of the ways they were going to do this was to give her a new costume and a new codename to replace the outdated "Marvel Girl" one. Cockrum went through a wide variety of looks for Jean before coming up with this excellent costume that also worked well when John Byrne changed the color scheme to make her Dark Phoenix. Cockrum's design for Ms. Marvel deserves a note here. It didn't make the list as it was a bit too skimpy of a costume, but otherwise, it was a great look (and of course, it also had a sash).
Mike Zeck came up with the actual look and it is a stunning piece of design. All black except for the prominent white spider. Rick Leonardi also did some tweaks to the costume and it soon became the most controversial, yet surprisingly popular costume change in comic book history. Fans were aghast at first but then really started to enjoy the new look. Eventually, the design was adapted for the villain Venom, with Spider-Man returning to his classic look. It is popular enough, though, that it still makes occasional comebacks.