I’d say that I saw this movie late night on UK Channel 4 around 20 years ago. From what I remember there was a couple living out in the wilds which had white caves and the lady seemed to like floating nude in the pools outside. For some reason there was a white giant in a loincloth perusing them. It was all quite surreal and I mistakenly thought that the film in question was The Silent Flute with David Carradine, but maybe this was the film that was shown beforehand.
War of the Colossal Beast (1958)?
The Amazing Colossal Man (1957)?
“Frankenstein’s Castle of Freaks”(1974)?
Terror! Il castello delle donne maledette
http://imdb.com/rg/an_share/title/title/tt0069851/
You can watch the entire movie on Youtube, but I remember a giant and a neanderthal man in this and one or both of them spy on skinny dipping women.
No, this film was definitely in colour.