Making paint that changes colour when you apply a magnets magnetic field

Changes colour by a magnets magnetic field and changes back to the colour it was when you go over it again.

Update: Better, using the two poles on a magnet. For example the north pole of a magnet makes the paint gray and the south pole of the magnet makes the paint white.

With a very small magnet you can even write or draw something

The paint should be non toxic and durable.