They were doing test shots for the makeup, so they filmed her with the green makeup on. The next day, the film came back from the lab, and Oliver had normal skin color.
The filmmakers were surprised, and the director gave the order to "paint her greener." So they painted her "greener" and tried again. The next day, the film came back from the lab, showing Oliver with normal skin color.
They finally realized that each night, the guy developing and printing the test film was freaking out at what appeared to be a woman with green skin. So, he would filter the light when making the print to bring her skin tone back to normal.
No one had told him that she was supposed to be green.