What are these green and black marks in my tallow?

What are these green and black marks in my tallow? - White Blank Notebook

I bought some tallow, used it a few times then left it in the fridge for a few months. As you can see in the pic it has developed some green and black spots.

What are these and what caused it? Is it safe for consumption? Can I discard the coloured bits and use the rest of the tallow? enter image description here

fat

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Images: Tirachard Kumtanom, Thirdman, Ketut Subiyanto, RF._.studio