Basically, when you can tell sides in a conflict by what they wear. It doesn't matter the specifics of what they wear, just that one side has a distinctly different dress than the other.
This is actually quite common in fiction. One example is wearing a uniform for any military, either in fiction or Real Life (since you need to tell who to stab/shoot at). This also means this trope can be enforced by an actual Dress Code.
Other times, it can be cultural dresses or the personal styles of the heroes and villains.
This can also apply even with Grey-and-Gray Morality. Just because you don't know which side is really the bad guys, doesn't mean you can't still tell one side from the other.
A Super-Trope to:
- Evil Wears Black
- Gas Mask Mooks
- Putting on the Reich
- Sensible Heroes, Skimpy Villains
- Shabby Heroes, Well-Dressed Villains
- Spikes of Villainy
- Sukhomlinov Effect
Compare Hollywood Dress Code, Color-Coded for Your Convenience, Good Eyes, Evil Eyes, Obviously Evil, Highly Conspicuous Uniform, Characteristic Clothing Colors, Slobs vs. Snobs, Alike and Antithetical Adversaries.
Not to be confused with Significant Wardrobe Shift.
- Claymore zigzags it: at first, it looks like the stylish, uniformed Claymores are the good guys protecting humanity from the amorphous, shapeshifting yoma. Then it turns out, they are Not So Different from yoma, after all. However, their real, much worse enemies are the Awakened Beings who don't wear special clothes, but each have a distinct appearance in their Awakened form (in contrast to Claymore uniforms whose only distinct feature is their symbols). Then, after the Time Skip, we get the Sexy Seven nicknamed so for their new sexy black uniforms. So now we've got the Good-But-Misguided uniformed Claymores working for The Man, the Good, rebellious, black-clad Sexy Seven, and the Ultra-Evil Awakened Beings, each with their distinct appearance.
- K: The Blue Clan, SCEPTER4, known as a policelike force in the series, has a very strict dress code. All members wear the same blue coat and are equipped with swords. Their chief adversary, the Red Clan, has no dress code, but most of its members dress like gangsters and rebels, putting them in sharp contrast.
- Sailor Moon: All Sailor Soldiers in the UNIVERSE share some semblance to this, even if it's just a Sailor Collar and some form of Tiara. When the final arc introduces evil ones, it's still easy to tell them apart. Heroes: same as always or bikini top, hotpants, thigh high boots, elbow length gloves (Sailor Starlights), and the Villans have...everything else.
- In the Tintin story Tintin: The Calculus Affair, a fight has broken out between the Syldavians, who all wear brown coats, and the Bordurians, who all wear grey coats and have shaved heads. Despite this, the Captain doesn't know which side to aim for, so Tintin just tells him to go for the ugliest mugs.
- Rogue Trooper - the Norts wear rubbery suits and gas masks, while the Southers wear harder armour and clear visors.
- The LEGO Movie: The Master Builders dress in colourful, out-there outfits which represent their free and rebellious attitude and are often related to pop-culture, whilst Lord Business dresses accordingly to his name with his minions in dark, enforcement related clothes to symbolise a stricter, more systemised nature. Hell, Good Cop Bad Cop is wearing an imposing black police officer's outfit and the Super Secret Police are all dressed in black.
- As in the picture, Agents in The Matrix dressed like government agents, while the good guys wore mostly black, stylish clothing.
- In the original Star Wars trilogy, the rebels had a variety of uniforms, and so did The Empire. It's just the styles of them were easy to tell apart.
- The Sith and the Jedi. Hell, even before his FaceHeel Turn, Anakin was wearing tons of black leather in sharp contrast to Obi-Wan's tan robes.
- In The Rocky Horror Picture Show, at first, Brad and Janet wear more conservative clothing compared to Frank N. Furter (who is in women's lingerie). Later in the film, when they are corrupted, they are stripped down to their underwear and also end up wearing the same clothing as Frank during the floorshow.
- The Dark Knight: The Joker used this trope for his advantage. The doctors were the Joker's men and the clowns were hostages.
- The Lord of the Rings and The Hobbit trilogies both use uniquely designed armour so that combatants are easy to tell apart in a fight. Naturalistic Art Nouveau shapes were used for elves, sharp angles and geometric designs represented the dwarves, Nordic and Viking-like designs were attributed to the Rohan (going with Tolkien's idea of the Rohirrim as, essentially, Horse Vikings), and Roman-esque armour with seabird motifs were used by Gondor (going with the striking parallels between Gondor and the Byzantine Empire, being a rump of a once-great empire, but one which retained considerable naval skill). For the villains, dark armour with horns and fur and a general slapped-on look were used for orcs, and Uruk-hai and Sauron's "Uber Orcs" had armour was still crude but felt more solid to show that they weren't messing around.
- Nineteen Eighty-Four: Members of the Outer Party, such as the protagonist Winston Smith, wear blue overalls. Members of the Inner Party wear black overalls. Children belonging to the Youth League wear red handkerchiefs, gray shirts, and blue shorts.
- In Steven Brust's Dragaera stories, Dragaerans in the Dragaeran Empire belong to one of 17 great Houses. Each House has its own colors, and most Dragaerans typically wear some variant of those colors. Jhereg wear grey and black, Dragons wear black and silver, Phoenix wear gold, and Orca wear pale blue and green. The House of the Yendi is the only one which doesn't have set colors. House colors become a plot point in The Phoenix Guards, when an independent-minded Dragaeran causes a romantic misunderstanding when she wears another house's colors.
- Wizards in Dragonlance, at least prior to the Second Cataclysm, had a strict dress code: Good wizards wore white robes, neutral wizards wore red robes, and evil wizards wore black robes. Raistlin' had to dye his robes when he changed sides and broke the rules by not officially declaring his change of colour to the Conclave.
- Don't forget brown. Brown robes meant that you didn't go through with the test.
- Terry Pratchett averts this trope on multiple occasions, most notably with Lady Margolotta from The Fifth Elephant . Fluffy pink cardigans are not standard vampire wear, not even when patterned with a bat motif, but Margolotta's manner of dress is almost certainly deliberately designed to make the unwary underestimate her.
- In The House of Night, when the Big Bad decides to take over the Vampyre High Coucil, she changes her colourful wardrobe for skin-tight revealing black dresses. It's also a case of Sensible Heroes, Skimpy Villains and she has Femme Fatalons to complete the look.
- Game of Thrones: Invoked in "The Laws of Gods and Men", when the defendant is brought in shackled like a beast even though the idea of him overpowering the guards and fleeing is ridiculous. His accusers also appear in their finest and most conservative attire to play up their nobility and innocence.
- Stargate Atlantis has each side wearing their respective military uniform, with a few off-worlders in native dress thrown in for variety. But flip the Matrix example for fun—it's the good guys who wear the regular military clothes and the Wraith who wear the leather.
- And going the other way, the expedition's baggy battledress contrasts nicely with the Genii and their habit of Putting on the Reich.
- In Stargate SG-1, it's pretty easy to tell Jaffa in full gear apart from everyone else. They were metallic armor that was mostly ineffectual against bullets and is mostly ceremonial. Different Goa'uld also have different styles of headdress for their Jaffa. Only two are shown on-screen: the falcon-headed guards of Ra's family (including Ra, Heru-ur, and Hathor) and the serpent-headed guards of Apophis (Ra's brother, by the way). The armor also makes a loud clang when marching, making them easy to spot from afar.
- A third type of headdress worn by Setesh's (AKA Seth) Jaffa is mentioned in a joke but never shown, as Seth has long ago been exiled.
- The metal mask things the Mind Control gas comes out of looked like they were made of the same stuff as Horus Guard and Serpent Guard helmets; they were probably Setesh Guard helmets. If they are, you can see where the jokes came from.
- Babylon 5 takes a rather literal Planets of Hats approach to this. The Centauri dress like the Prussian military, the Narn favour leather oddments dyed and visibly stitched together, the Minbari go for priestly robes, and later, we see the warrior caste use somewhat more functional clothing. The humans start in the same outfits, wearing high-collared tunics for the military (not entirely dissimilar to some current forces' uniforms) and weirdly-modified 90s clothing for civilian wear (the print patterns and preference for band collars for men are particularly Zeerusty), but then splinter and argue over the clothing bin—leading the early-90s Zeerust to expand to the military side.
- Played for laughs on That Mitchell and Webb Look where the Nazi officers start wondering if the skulls on their uniforms make them the bad guys. At one point, one of them accuses the other of being taken in by Allied propaganda, pointing out that naturally the Allies would be trying to frame them in a poor light. The other retorts that while this might be the case, the Allies didn't also get to design their uniforms.
- Star Trek: Deep Space Nine, the Jem'Hadar are an easily recognizable race of soldiers in conflict with Starfleet with a gray-on-gray motif for their uniform, equipment, and body armor. When the good guys need to team up with a Jem'Hadar squad to fight other Jem'Hadar, the "bad guys" for this episode were kind enough to wear an all-black vest so the audience could figure out who was who.
- In Over Blood, the good guys wear "jackets" that are too small for them. The bad guys don't.
- Republic troops in Knights of the Old Republic wear orange, yellow, and black, while Sith troops wear chrome or metallic red.
- All gang members, police and pimps in the Saints Row series have the same kind of uniform which makes them easy to spot.
- Grand Theft Auto: San Andreas combines this with Color-Coded for Your Convenience with street gang members (Grove Street Families green, Ballas purple, Vagos yellow, and Aztecas cyan) so that you knew who would shoot at you on sight (Ballas and Vagos).
- In the Paper Mario series, you can tell which Koopas are good and which aren't (at least in the first three or so games) by whether they're wearing sunglasses or not (the former are the evil/brainwashed/villain versions). The evil ones also have red shells and spiked arm bands and collars like those worn by Bowser
- Some RTS games, such as Age of Empires III, will avoid using two of the same nation in randomized skirmishes to avoid confusion when not using the trinary color option. For a non-opposing example, upgrading your units gives them significant cosmetic changes that allow skilled players to identify the tech level of opposing units on sight. For example, upgrading Age of Mythology's Ulfsarks to the highest rank makes their bearskin hats vividly white, as opposed to the usual brown.
- This is a popular trope in video games, particularly first- and third-person shooters. This is because the player needs to be able to quickly distinguish enemies from allies
- The mercenaries, French soldiers, and rebels in Cry Havoc all wear different styles of gear. The mercs wear green or olive armor that is much larger and bulkier than the French's tan and brown vests. The rebels wear much brighter colors with light vests and armor or none at all.
- Homestuck: This is a design feature of Sburb, in which natives and dreamers of Derse and Prospit dress according to their planet. Subverted in the kids' session, when the Black Queen liked harlequin colors enough to enforce it in uniform, and apparently so did the White Queen, as both Black and White armies dress similarly. The Kings still wear their own color.
- There are still differences in color between the two: the Prospitans usually going for light blues, yellows, greens, and pinks, while Dersians use darker versions of those colors with red instead of blue and purple instead of yellow.