I'm slowly working my way through the comments you've left me over the last few months, and I'll be posting those I think would appeal to a larger audience over the next little while. If you have a question, please comment on a relevant post, regardless of how old it might be, and I'll do what I can to answer it!
Pumpkin seed oil: A whipped butter, Adele asks: This is my favorite body butter, but I saw that in time (after 2 weeks of use) it turned its color from light green (due to the pumpkin seed oil which was unrefined cold pressed) to a more brownish color, which I don't like. What can be the cause? Oxidation or the temperature (which was above 20 Celsius degree in the room I kept it)? Thank you!
I love this recipe so much, so I'm glad someone else loves it, too!
There are so many reasons a product can change colours, and most of them are pleasant and okay. For instance, in the picture above, a tiny change in oils changed the colour. Add something like sea buckthorn or rosehip oil that has a very orange hue, and you'll have yourself a darker coloured product. Add something like fractionated coconut oil or squalane, which are colourless, and you've got yourself a clear or very white product. Something like unrefined hemp seed oil could make something quite green, and so on.
Powdered rosemary extract has coloured this shampoo a deep green, something you can avoid by using a clear, liquid extract instead.
This is the risk in using botanically derived ingredients: A different climate, a different growing season, a different soil, and so on can lead to very different colours from the last batch you bought. In general, if you see a brown or green colour in the ingredient, it'll show up in the product. There's nothing wrong with that, but if you were looking to make a colourless, clear shampoo with green tea extract or a facial cleanser with grapeseed extract, you'll be sad with the end result. (I love the colour of that cleanser so much!)
Related: My article in Handmade Magazine: Understanding the Vanillin Villain
In the case of your green oil turning brown, I think you're right - there's oxidation going on, but it's not a horrible thing. You could add an anti-oxidant like Vitamin E to slow down that process, you could use a more refined, less coloured oil, or you could keep it in a cooler place.