Black and red. In western culture, these are the two most sinister colors, as red typically conveys the meaning of blood or anger, and black is that of darkness or death. Being a very visually striking combination, they can also convey a sense of power. Together, they can also give the impression of burning coal or wood, i.e. "fire and destruction". Sticking to these two colors is common for designers who want to create something as sinister as possible.
A favorite color for villainous characters to dress in (when they aren't wearing purple, green, and orange). For example, most Ominous Opera Capes are a case of this: black on the outside, red on the inside (which is really common with vampires). It should be noted that this trope is not just a list of villains wearing black and red; it can apply to non-character elements as well. For example, this is common for the covers and credit sequences of horror books, films, and games, to show that a work is Darker and Edgier.
Historically, red and black (along with white) were heavily used in Nazi Germany's symbols, so The Empire displaying these colors in its flags and architecture may give the impression of Putting on the Reich, even if the associated characters themselves don't wear them. See Red and Black Totalitarianism.
Dark Is Not Evil can also apply with Anti Heroes and even Villain Protagonists heavily using a red and black color scheme as a visual reminder that these people, no matter how much we are supposed to identify with them, are not "good guys". Or that the concepts associated with this color scheme, such as darkness, blood, or fire, are not that evil to begin with. Can also be used to benefit from Evil Is Cool without resorting to actual evil. If a heroic character wears this, they may be an example of a Terror Hero, or of Good Is Not Nice at the bare minimum. It's not uncommon for cases of this to be juxtaposed with a group of characters represented by blue and white. If the hero is represented by the colors blue and white, The Rival or an Evil Counterpart may have the black and red color scheme.
A Sub-Trope of Good Colors, Evil Colors. A Sister Trope to Evil Wears Black.
Compare Dark Is Evil, Grayscale of Evil, Red Eyes, Take Warning, Red Filter of Doom, and Obviously Evil, as well as Big Red Devil. Contrast Gold and White Are Divine, Heavenly Blue, Red Is Heroic, Movie Superheroes Wear Black, and Primary-Color Champion, where blue takes the place of black. Compare or Contrast Dark Is Not Evil and Red Is Violent for anti-hero/anti-villain examples, as well as Mysterious Purple for people with less defined and often obscured allegiances and moral leanings.
See also White and Red and Eerie All Over, which is portrayed as ghastly in addition to being sinister.
Note: In case of characters, this trope mostly applies to villains and anti-heroes.
