because of the Red Woman's sorcery
Game of Thrones Season 3, Episode 10
A RED priestess from Asshai
has come to see you.
Game of Thrones Season 7, Episode 2
nothing flashed RED,
so that's gotta mean it's okay, right?
Breaking Bad Season 4, Episode 9
You killed a hostage,
you stepped over the RED line,
Money Heist Season 1, Episode 9
I got RED.
The Big Bang Theory Season 5, Episode 10