Invisible Subtle Difference

""The man has only one look, for Christ's sake! Blue Steel? Ferrari? Le Tigra? They're the same face! Doesn't anybody notice this? I feel like I'm taking crazy pills!""

- Zoolander

The cast is trying to choose among several items that are, they insist, subtly different in some way. One character is fed up with their dithering, because as far as he or she can tell, they're all the same. Sometimes inverted, with one character insisting on a difference that nobody else perceives. Either way, and whether or not a difference actually exists, usually the audience can't see the difference.

Most commonly seen with subtle color differences, but can be anything, even identical-seeming people.

Generally Played for Laughs. Often appears with Limited Wardrobe, Evil Twin, Planet of Steves, Those Two Guys, and/or Only Sane Man. Compare and contrast Shell Game, Spot the Imposter, Needle in a Stack of Needles, and I Am Spartacus. This may be used to indicate Hyper Awareness, or as one of the components of a Sherlock Scan.

Anime and Manga

 * In K-On!, Sawako-sensei is able to tell that Ui is impersonating Yui because her breasts are slightly bigger.
 * In Pokémon, each town has an Officer Jenny and a Nurse Joy, who all look identical—but Brock can tell them apart. Similarly, all mons of the same variety look identical to the audience, but Pokemon trainers can distinguish their five magnamites, or whatever.
 * In Pokémon Black and White, a young woman with four Patrats is aware that she can distinguish them and the player can't—so she challenges the player to a Shell Game with them.

Comedy

 * A well-worn gag: wife asks husband to decide between two (or more) different colors (usually, but not always, of paint for the house); husband can't tell the difference.

Comic Books

 * In an early Mad Magazine parody of Archie, Archie reacts angrily to a claim that Betty and Veronica are alike, claiming that they are very different. In the next panel, the two girls are drawn identically except for hair color. Their hair styles, poses, even the zits on their faces are the same.
 * The Smurfs make distinctions between two "smurf" words that all sound identical to humans. It doesn't show in most works because they're alone, but this is usually seen when Johan and Peewit are present.
 * In the Don Rosa story An Eye For Detail, Donald Duck is able to tell apart his identical triplet nephews (Huey, Dewey, and Louie). Uncle Scrooge tries to find a way to profit from this talent of Donald's. Hilarity Ensues, naturally.

Film

 * Juno uses the paint gag described under Comedy.
 * Watchmen: Ozymandias claims he can see subtle distinctions in Dr. Manhattan's face, showing his emotion, which to the average person are invisible. As he says this there's a shot of Dr. Manhattan's face, in which we see no emotion (but presumably Ozymandias can).
 * Zoolander provides the page quote: after an entire movie's worth of people gushing about Derek Zoolander's variety of "looks," one of the villains can't take it any more.

Live Action TV

 * Babylon 5: Nobody can tell the ten Zathras brothers apart, or hear the difference in their names, but the Zathrases themselves.
 * Frasier: Frasier offers Roz advice on what color to repaint her house. He looks at three tile samples and proclaims them subtly different shades of off-white. Then she flips them over and advises him to look at the colored side.
 * Happy Days: Ralph and Potsie are living downstairs from a pair of twins, Daisy and Masie. Ralph thinks they look exactly the same, but Potsie says Masie has whiter teeth.
 * Home Improvement: Tim and Jill are picking out bathroom tiles. Jill insists they're different colors, Tim sees them all as white. Al, however, agrees with Jill.
 * Parks and Recreation: Tom Haverford and Jean-Ralphio are picking out black memorial ribbons. Jerry thinks they're all the same, but Tom and Jean insist they are a variety of shades, such as "Lost Soul" and Midnight Panther".
 * The Red Dwarf episode "Me2" has a scene where Rimmer is having a corridor repainted from "military grey" to "ocean grey". Lister can't tell the difference, and neither can the audience.
 * There was a Saturday Night Live sketch about two Americans, Mike and Beverly, meeting a bizarre foreign couple (as in, an odd mishmash of Japanese and Scandinavian stereotypes), named Nooni and Nooni. Any time Mike said either name, Nooni or Nooni would immediately point out that he'd gotten them mixed up. Even though the only difference between the two names was which syllable was emphasized (and Nooni himself wasn't consistent on which name received which emphasis).

Web Comics

 * Xkcd discusses it.

Western Animation
"Phineas: That's just a duck with a tail taped on!"
 * Archer: Archer is shown purchasing and bullying his butler about several identical black cardigans, which he insists are all different colors.
 * As mentioned under Comic Books, Donald Duck can tell Huey, Dewey, and Louie apart. Sometimes Scrooge McDuck can too. Usually no one else can, unless they're wearing differently colored clothes.
 * The Penguins of Madagascar: The lemurs need to install a cooling device on the zoo's furnace before it explodes. The device has seven colored knobs; according to Kowalski, who is giving instructions by telephone, they are red, crimson, scarlet, brick, salmon, ruby and rose. The lemurs are only supposed to turn the scarlet knob, but to them (and to us) they just look the same shade of red.
 * Phineas and Ferb episode "Oh, There You Are, Perry": Perry is forced to leave home by the agency. The boys, trying to find him, make a device that calls platypuses, and are immediately surrounded by dozens. The boys find a reason to believe none of them is Perry, even though to the viewer's eye they're exactly alike. All except for one:

"Lisa: I'd like 25 copies on Goldenrod. Clerk: Right. Lisa: 25 on Canary. Clerk: Mmhmm. Lisa: 25 on Saffron. Clerk: All right. Lisa: And 25 on Paella. Clerk: Ok, 100 yellow."
 * The Simpsons episode "Lisa the Iconoclast":


 * The Venture Brothers: in the episode "Dr. Quymn, Medicine Woman." Hank was indiscriminately interested in both of Dr. Quymn's semi-identical twin daughters, Nancy and Drew, even though he couldn't tell them apart. Dean could tell them apart, and tried to clue Hank in, but it didn't help.

Real Life

 * Identical twins look very similar, but their families can almost always tell who is who.
 * Identical twins often adopt distinct hairstyles or wardrobes, to prevent people from confusing them.
 * Some studies claim that women are, on average, better at distinguishing similar colors from each other than men are; this perhaps justifies the paint gag described under Comedy.
 * Some audiophiles insist that they can hear a difference between music reproduction techniques which, scientifically speaking, should produce exactly the same sound. This has been known to cause flame wars.