Originally Posted By: 69GTX
I wonder if that could be because the background is black plastic?
It's because you're looking through more of the oil, as compared to on the dipstick or even in the stream coming from the drain hole. There is more oil between the light source and your eyes, so less light passes through it. It's the same reason some clouds look black while some appear to be white. If a cloud is more dense than another, less light passes through, so the cloud appears to be darker.
(I didn't watch the video; my apologies if this was in reference to, or mocking, something in the video.)