In some regions of Central Europe, salad dressing is made with pumpkin seed oil, which has a strong characteristic nutty flavor and striking color properties - in the bottle it appears red, but it looks green in a salad dressing.
Samo and Marko Kreft's paper examines the remarkable two-tone (or dichromatic) color of pumpkin seed oil, by the use of a combination of imaging and CIE (International Commission on Illumination) chromaticity coordinates. The paper also explains why human vision perceives substances like pumpkin seed oil as dichromatic or polychromatic (exhibiting a variety of colors).
Two phenomena explain the perceived shift in color of pumpkin seed oil from red to green:
First, the change in color is due to a change in oil layer thickness.