An easy way to tell a villainous (or sinister) character apart from the protagonists, other than giving him/her a Red Right Hand, is making their eyes red. If they don't start out evil, there's a chance they become so over time or perform full-blown Face–Heel Turn. It's not the same thing as the "Red Eye" phenomenon in photos, but if cameras could detect evil, or danger these would be the first people they'd catch.
Even those who are not truly evil or dangerous are often thought to be so by characters In-Universe.
In the progressive algorithm of "Uh-Oh" Eyes we have:
Supernatural Gold Eyes < Red Eyes, Take Warning < Hellish Pupils < Glowing Eyes of Doom
Those with glowing red eyes are almost without exception thoroughly evil or, at least, very dangerous. The "almost" section goes to those whose red eyes serve as a marker for their Elemental Powers, typically fire.
A subtrope of Technicolor Eyes. May be part of Evil Albino, or averted/subverted by the Heroic Albino, although most humans with albinism in Real Life have pale gray or blue eyes.
Compare Glamour Failure and Red Is Violent. Contrast Red Is Heroic.
Not to be confused with the film Red Eye or the liquor. Sometimes a part of Burning with Anger, and thus a harbinger of wrath.
It should be noted that trope is NOT just for characters who have eyes of this colour, but when the colour actually indicates the character is evil or dangerous, or presumed to be because of their eye colour. Please do not add characters who just happen to have eyes of this colour without the proper reason behind it.
|“||I'll show them, nobody makes a fool of Jack Frost. When I get through, they'll be no more Frosty the Snowman. (Laughing)||„|
|~ Jack Frost showing red eyes while plotting revenge.|
|“||Please! Once I enslave the universe, I won't need the likes of you. It'll be all Zurg all the time! 24-7! Zurgie heaven!||„|
|~ Zurg with glowing red eyes over his success.|