How would you expect the temperatures of the lake and sand to compare just
Since the sand absorbs better than the water, it will also emit radiation better than the water. Thus the sand will be cooler than the water at daybreak.
How would the differences between the lake and sand compare if the sand
Since it would absorb even better, the sand would be even hotter in the daytime. Since it emits better it would be even colder at daybreak.
Would a dark roof on a house make the house more or less heat efficient in the winter?
In daytime it would absorb sunlight better than a light roof, helping to keep the house warmer. At night it would emit radiation better than a light roof making it colder than a house with a light colored roof.