[pdurrant]

Originally Posted by LazyScot

Spoiler:

White.

You can only ever reduce the number of white balls by 2, never by 1 (if you take out one white and one black, the white is always returned). Thus sooner or later you will have a single black ball left in the pot, with an arbitrary number of black balls. At this point you will never throw away the white ball, hence the answer of white.

And another right answer with the correct reasoning.

Spoiler:

(Although at one point in your explanation you've written "black" instead of "white".)