it may seem as though we have the answer but i would not guarantee that until i see the fluid relating to part number at bmw dealer .
the fluid in the link had vw/audi part number and my fluid is not very dirty compared to the used fluid in that link.
my fluid resembles Duckhams hypergrade motor oil , if you are old enough to remember that blue/ green oil .
there is a possibilty that the factory put additive in transmission so that could explain the colour.