Yes, it does! The pool will get warmer than if you put the black garbage bags on it. The reason is that sunlight will come and heat your pool, and this incident will cause an increase in temperature.  Without it, it would release the heat back into the air, and the pool would stay cool throughout the day. But if you use black bags on top of your pool, they would be directing that heat into pulling up the pool water temperature. In other words, black color absorbs a high level of heat from the sunlight and transfers it into the pool water, becoming warmer. And as a result, this becomes a positive outcome of placing black garbage bags over your pool.