Duplicate the base layer. This is going to be your first color. Start with the color with the most area. In this case, it would be the skin of the model. To get a good sampling of color, we need to locate an image that has similar content and darkness levels. Here I've chosen a picture of a woman in a similar dark setting. Using the eyedropper, pick up a mid-tone. That means we're looking for the tone between the brightest and darkest points. Here, it would be on the apples of her cheeks. After picking up that color with the eyedropper, open the palette and copy the hex number for that color, you'll need it later. Now we want our edge tones. Pick up a dark tone from the image (not black, you want color), then rotate your color palette and pick up a highlight color.