Euphemistically, idiomatically, this speaks to bruises.
Wendy is wearing black and blue when she prepares dinner (No.29) while listening to violent news stories about men and women.
Continuing to No.30 where she approaches Jack mid-work, Kubrick creates a shot that has her juxtaposed between two dark curtains. Combined with her blue outfit continues the connotation of abuse with Jack.
In this image · No.18
Black + Blue
The pipes bring together red, white, blue, and black. Red, white, and blue signify America; black and blue invokes bruises and being beaten.