[Stratoscope]

Bingo! Now that you jogged my memory, I can confirm this.

The next question is why you need a white outline around the black arrow.

This is easy to answer: if you didn't do that, what would the black arrow look like against a black background?

[justsomehnguy]

Some DE solved that by having an inverse outline.

[jsjohnst]

Took me a really long pause to think up what DE meant, so to save others from similar waste “desktop environment”

[bmicraft]

I'm pretty sure even on windows there is the option of having the whole cursor be the inverse of the background

[whywhywhywhy]

The format has a special color for it, you can mix inverse pixels anywhere in a classic windows cursor IIRC