It's well known that Pumpkin Seed oil is dichromatic - a thin layer of it is a greenish-yellow but a thicker layer is a dark red.
Yesterday I noticed that another oil seems to have a similar property. There was a tiny drop of Rape-seed left in the bottom of the bottle and I noticed it appeared green, although in bulk the oil was not green at all but a golden yellow. Here it is - definitely green.
Here is what a bottle of this oil looks like when full - definitely yellow.
What's going on, why is the colour different? I think the explanation, very roughly, is that the light passing through the oil is made up of different colour components. The light is partially absorbed by the oil but some colours are absorbed more than others. If the light has to travel a significant way through the oil the blue and some of the green get preferentially absorbed and the remaining components are perceived as yellow. But if we only have a thin layer most of the blue and green survives and now the colour we perceive is green.
I first learned about the properties of Pumpkin Seed oil in 2021 and wrote a blog post about it then/ I bought some Pumpkin Seed oil back then and tried it some experiments. Here's a photograph I took. I hope you can see that at left where the oil is deeper it has a dark red hue, whereas at right where is only a thin oil layer the colour is green/
