Allow the ball provided to roll down from the starting point marked. Observe the ball till it falls into the bottom hole.

What did you observe? 
The black plate is the hottest whereas the white plate is the coolest. The other coloured plates emit different amount of heat.

The science behind it :
Black surface always absorbs and radiates more heat. Hence it is the hottest one. On the other hand, white surface reflects the heat. Hence it is the coolest one. The plates covered with other colours absorb or reflect different amount of heat according to their wavelengths.