This is Alain Robbe-Grillet's first colour film. Apparently he had the resources to make them before this, but deliberately chose to work in black and white because he hated the colour green. Or at least, so the review at Electric Sheep Magazine tells me (warning: images in their review contain nudity).
Certainly Eden and After is entirely bereft of that verdant hue, instead being saturated with blues and whites, highlighted from time to time with blood red splotches. And yes, the use of the term 'blood red' was a very intentional and specific one.
A group of young French dilettantes assemble at a cafe each day and play-act various debauched or macabre scenarios: rape, suicide, murder and the like. Their unsavory games remain just that, however, until the arrival of a stranger known as 'the Dutchman'. He escalates their activities significantly, to the point that the play-acting begins to blur more and more with reality. Our central character, Violette (played by the gorgeous Catherine Jourdan, who was apparently cast only 3 days before filming started) is stalked through the canal docks by shadowy figures and then finds the Dutchman lying dead ... only for his body to be gone when she takes her friends there later. The only proof of her story is a postcard she found on his body.
Violette owns a valuable painting, and the postcard appears to depict the building on which it was based. So when the painting goes missing, Violette believes she will find it again at the location on the card, and travels to North Africa to locate it. This also initiates a twenty minute or so stretch with a lot of nudity and bondage-themed imagery, which I imagine could be either a positive or a negative factor depending on the viewer, but definitely seems like something you should know about ahead of time.