You can throw out any number of explanations for the enduring popularity of superheroes - the flashy, larger-than-life battles, the never-ending soap opera storylines, the desire of readers to immerse themselves in worlds where good and evil are easily delineated, etc. But part of it has to be the costumes. Superhero costumes are inherently bold and eye-catching. They're designed to be plastered on the cover of a comic and sell it to any random 10-year-old that wanders by. Not that many 10-year-olds are impulse-buying superhero comics these days, but that's a topic for another column. That begs the question, what does make for a good superhero costume?

In some cases more literally than others. (Art by Alex Ross)

A page from FF. (Art by Mike Allred)

(Art by Jim Lee)

Nope. Nope. Nope. And nope. (From Jim Lee, Man of Steel, and Injustice)

These two get along just fine without the external underwear. (Art by Joe Madureira)

As I see it, there are a few essential qualities. They need to be striking but simple. Superheroes appeal to our innate love of the human form. They wear costumes made of this entirely outlandish spandex material that somehow sticks impossibly close to every muscle and curve of the body but still hides their naughty bits (or depending on the target audience, not even that). So it's almost like watching Greek sculpture come to life and take flight.Good costumes also have strong iconography. Most heroes have a logo or defining visual characteristic, whether it's Superman's S-shield, Batman's bat emblem, Spider-Man's webbing, Wolverine's tiger stripes, or even something like The Question's faceless mask. Strip away everything else, and that icon easily and instantly identifies a hero.And there's also the element of color. The eye is naturally drawn to the bright hues and contrasting colors that superheroes have in abundance. Originally, this use of color was born out of necessity. The archaic printing technology that comics publishers were forced to rely on for much of the 20th Century (which basically involved overlaying colored transparencies on top of black-and-white art and photocopying the whole thing) forced artists to stick to bright, simple hues that were easily distinguished by the printer. And that's why we have so many characters sporting reds and blues or greens and purples or yellows and blacks.But even now that digital coloring is the norm, these contrasting colors persist. If anything, the costumes are even more eye-catching thanks to improved technology. A recent issue of FF even launched into a metatextual discussion of superhero costume colors and how heroes and villains use color to distinguish themselves. Heroes tend to flock to the primary red, blue, and yellow colors (Superman, Spider-Man, Iron Man), while villains stick to the secondary green, purple, and orange colors (Green Goblin, Doctor Doom, Lex Luthor). It's not a 100% consistent rule, but I'd argue that very often, those characters who do borrow from both ends of the spectrum (Magneto, Hulk, Sinestro) do so because they're more morally ambiguous.The standards of the day may change. Capes and masks may fall out of vogue. But every good superhero costume has those three essential qualities - form, iconography, and color.So with all that in mind, it's been interesting to watch the transformation of superhero costumes over the past couple decades. We've seen Marvel and DC make a number of attempts to modernize and update their superhero costumes. Part of this is due to the rise in popularity of superhero movies. The X-Men comics in particular saw a drastic visual shift in the years after the first X-Men film debuted. Part of it is due to the rising age of the average comic reader/superhero fan. Comics are no longer marketed towards kids, and so the industry has somewhat self-consciously re-examined how it portrays these iconic heroes. Iconic costumes that have stood the test of time for decades are suddenly, and sometimes drastically, being redesigned for a more contemporary audience. And naturally, there have been plenty of successes and failures along the way.Nowhere has this process been more interesting than with Superman. The traditional conception of the superhero really coalesced with Superman's debut in 1938, and his costume set the gold standard for everything that came after. He had the powerful physique, the logo displayed proudly on his chest, and bright, contrasting colors - form, iconography, color. And he had all the accouterments fans have come to expect - the cape, the boots, and the trunks or "underwear" outside his pants. These trunks are a relic from the outfits worn by early 20th Century circus strongmen. At the time, the trunks symbolized strength. These days, they're a relic publishers would just as soon leave behind.The problem is that I have yet to see a case where losing the underwear has actually improved Superman's look. Many artists and costume designers have tried. Just look at Superman's New 52 costume, the suit from Man of Steel, or the two versions of Superman from the Injustice video game. Each costume has ditched the trunks and tried to replace them with other elements. New 52 Superman has a red belt. Man of Steel's Superman costume has extensive piping along the sides. Evil Superman from Injustice has a giant splash of red on the torso and legs. And still, something always seems like it's missing.The problem is that ditching the trunks throws off the color balance of the costume. It's not simply the contrasting red and blue colors that make Superman's costume so eye-catching. it's also the carefully honed balance of red and blue. Superman's body is covered mostly in blue, but between his trunks, boots and cape, there's just enough red to bring everything into balance. Losing any one of those elements throws the whole thing off. Batman has the same problem in the New 52. He too lost his underwear via continuity wipe. And no matter how many extra lines and armored plates are added to the Batsuit, it looks odd without that familiar area of black to offset the grey.Again, it's all about color balance. Superheroes don't need that external underwear to achieve an iconic look. Just look at Spider-Man. Steve Ditko designed one of the most iconic costumes ever with Spider-Man, and he did it by eschewing the cape and trunks popularized by Superman, Batman and their ilk. As long as you pay careful attention to color balance and shapes, you can design a terrific costume without the need for capes or trunks. Wolverine's Astonishing X-Men is an excellent example. Artist John Cassaday took the familiar tiger stripe costume that had been a mainstay in the '70s and '90s, played around with the shapes and lines, and wound up with something suitably modern. It paid homage to Wolverine's classic look, but made it more elegant and modern. And it's not surprising that that costume (despite random alterations here and there) stuck around for a full decade, only finally being retired last week with the launch of Wolverine Vol. 6.