The color of blood, embers, and stop — warmth at its most urgent; first of the named hues.
Old English read (red), from Proto-Germanic rauthaz, from a Proto-Indo-European root meaning red or ruddy; red is among the oldest named colours in the language, tied from the start to blood and to fire.
The colour of blood, embers, and stop — warmth at its most urgent. The root's age matters: red was likely the first colour any language bothered to name at all.