What's the deal with the red in "The Sixth Sense"?

M. Night Shamalyan uses red to symbolize that something "supernatural" is going on or is about to happen. If you look at his other films, he often drops clues that represent a repeating theme. If you saw The Village, you might remember that red and yellow are important in the story (red represented "Those we don't speak of" and yellow was the safe color). Water was important in Signs. Long before they discover that water will kill the invaders, the son comments that the daughter is picky about her water, and she's constantly asking for new glasses of water, which she leaves all over the house because they "taste funny."

It's a pretty old storytelling convention, actually.

It's not the only one, The Shining used red anywhere bad things were going to happen, (so basically most of the interior of the hotel is some variation of the color red,orange or burgundy).

The Matrix used black and white for almost everything and everyone except when main characters were involved, the captains all wore dark purple. The rules of Zion wore blue and gold, and at one point Trinity brings a royal purple cloak to Neo (a coronation) of sorts.

in the director's notes on the dvd - it symbolizes when he (bruce's willis's charactrer) is dead and present but unknown to him - kind of a signal or symbolism for him to recognize - for instance the RED rose at the dinner table when he sits down and she just gets up and leaves.

That is M.Night's trademark. Everything in the Unbreakable was purple. He does it during the parts that have a deeper meaning.

The red color symbolizes blood and therefore death. Which in turn is a link to the supernatural.

the director did it on purpose to highlight moments in the movie when there would be something to do with the dead

maybe it is sybolising the blood from when he was shot... like a subliminal message trying to point to the fact he is really dead...

or maybe M Night Shylaman just likes the colour.

It was to symbolize death, considering Willis was dead the whole entire movie.

and kudos for spotting that, i had to watch the directors commentary for that scenario lol.

To show it's a horror movie

symbolism.

because of what is revealed at the end of the movie about kid's doctor.