Written and directed by M. Night Shyamalan, The Sixth Sense tells the story of Cole Sear (Haley Joel Osment), a boy who communicates with the dead, and Malcolm Crowe (Bruce Willis), the child psychologist who tries to help him. The big twist is that Malcolm Crowe is one of Cole's visions of the deceased. However, the filmmaker provides several hints to the big reveal using the colour red as a signifier of the supernatural encroaching on the modern world.
If you look closely, the opening sequence of Us uses red to symbolize a similar overlapping of realms and to underscore many of the film's traumatic moments.
You can watch The Sixth Sense on Netflix.