Researchers at the University of Ljubljana in Slovenia have solved the mystery behind why people occasionally see things change colour before their eyes.
Samo and Marko Kreft of the university, who conducted a study using pumpkin seed oil, say that it happens due to the unique makeup of the cells in the eye's retina, and specific physical properties of substances themselves.
In the study, published online in Springer's journal Naturwissenschaften, the researchers examined the remarkable two-tone colour of pumpkin seed oil by combining imaging and CIE (International Commission on Illumination) chromaticity coordinates.
The study also explains why human vision perceives substances like pumpkin seed oil as dichromatic or polychromatic.
According to the researchers, two phenomena explain the perceived shift in colour of pumpkin seed oil from red to green. Firstly, the distinctive change in its colour shade is due to a change in oil layer thickness, for the oil changes its appearance from bright green to bright red as the oil layer thickens.
They say that the observed colour is neither dependent on the angle of observation nor on the direction or type of light.
Secondly, say the researchers, the shift in colour is due to the unique characteristics of the cells in the human retina.
The human eyes have two types of photoreceptor cells-rods and cones. The researchers say that cone photoreceptor cells function well in bright light conditions, and are also the basis of colour perception in our visual image.
They say that it is the presence of multiple classes of cone cells, each with a different spectral sensitivity, which gives people the ability to discriminate colours.