By These Ten Bones by Clare B. Dunkle. New York: Henry Holt, 2005.
The weather changes frequently in the Highlands, and this completely changes how the Highlands look. When the sun is shining, the hills are a pleasant green. (A cloud is moving across them in this photo.)
But the hills look black and ghostly under a cloudy sky, and the clouds are are often very low.
The same thing happens to water, which is blue and sparkling under the sunshine.
Just a couple of hours later, it can be drab and gray.
Frequently, the clouds cut off the hills altogether, so that they cannot even be seen. Sometimes they appear and disappear as low clouds go by. And even in summertime, mist and fog are common.