Returning Explorer Puzzle

Puzzle
An explorer walks:
 * one mile due south,
 * one mile due east,
 * and one mile due north.

He finds himself back where he started.

He shoots a.

What colour is that ?

Solution
White.

Proof
The explorer starts from the North Pole.

Every direction from the North Pole is due south.

Walking due east keeps him the same distance (one mile) from the North Pole.

Walking due north takes him back to the North Pole again.

The bear, as a consequence, must be a.