The cavemen footage is from a Filipino movie shot in 1965. The new US color footage was shot in 1966. The film itself wasn't released until 1970.
The Filipino film Tagani (1956), which forms the basis of this film, was made in black and white. As drive-ins at the time were clamoring for color features, the black and white footage was tinted using a process which was hyped as Spectrum X. All it did was convert certain scenes into bright single colors (red, green, yellow) that alternated between scenes.
This film is a mixture of newly shot footage and clips from a Filipino horror movie called Tagani (1956), One Million B.C. (1940) and Unknown Island (1948).