Black Stuff in the gear oil

Today i changed the gear oil while i'm filling my transmission i found something like very fine black particle or sediments swimming with the oil this stuff only shown when i'm trying to get last drop of oil from the bottle but when the bottle is full of oil and filling the transmission, the oil is crystal clear, i don't know, Is that normal? Hint: the bottle is black i don't know, Is that from the plastic of the bottle ? the date on the bottle is 3/19 i guess is not old

Type of gear oil is: Meguin 75W-90 API GL4+
Hedgesville, WV
I dont know what it is either but I have seen it in almost every type of oil at one time or another. The only one that I have not seen it in is hydraulic oil. It must be some additive pack sediment.