Well you contradict yourself, since there’s no such thing as purple light, it must be as much a colour as black is. Have you considered your third-grade gotcha might not be quite nuanced enough for the real world? Or that the science of colours might be a little more complex than you first thought?

Is purple a colour?

If the arm can bend, the car and the magnet could move towards each other until they come together, moving the car at max a few centimeters. If the arm doesn’t bend, the car is pulled as much forward as the magnet, and therefore the arm and in turn the car itself, is pulled forward, leaving the whole system stationary.