As OpenCulturepoints out, Kubrick was obsessed with red.
But he used it to provide all sorts of different subtexts. The website cites Abject Terrors: Surveying the Modern and Postmodern Horror Film by critic Tony Magistrale:
[T]he particular use of red as the keynote color in Kubrick's cinematic palette speaks directly to cinematic meaning: The color red underscores varying levels of physical and psychological violence present in Clockwork, The Shining and Barry Lyndon; forces the viewer to make a connection between HAL and demonic energies in 2001; and is associated with the carnal sexuality that is present in nearly every sequence of Eyes Wide Shut.