Why does a compass have a red arrow and a white arrow?

Answer 1

compasses point because of Earth's magnetic field

for example, if you think of the Earth as having a big bar magnet in it, then the South end of the magnet would be in the North Pole and the North end in the South pole.

then, the natural "Opposites Attract" rule comes into play.

Answer 2

A red arrow is pointing where North is, while the white arrow is pointing to the South.