How, then, does color film render color? Color film contains three layers of photo-sensitive emulsion that are sensitive to different wavelengths of light: red, green and blue, respectively. The layer that is sensitive to red light is normally applied first, followed by emulsions sensitive to green light, and then blue light as the topmost layer.

Adding dyes to silver halides makes them sensitive only to specific wavelengths of light. When color film is exposed, each photosensitive layer absorbs light of a specific wavelength. Color film contains dye couplers, which, on development and fixation, become yellow, magenta or cyan, the three colors that are complementary to blue, green, and red. This is why a red apple appears green in a color negative. When light is shone through such a color negative onto color printing paper, the yellow, magenta and cyan colors in the negative create complementary colors in the paper, thus recreating the original colors of the subject photographed. This is the principle behind the dye coupler method of creating color images.