In this preset for Color Efex you can indicate good accents in the sky, especially with clouds. You can do that locally with control points, per effect. Look for one at the introduction of the NIK presets. The video is called "Color Efex Pro 4 - Working with Control Points". You can of course also apply the preset in its entirety. Below you can see an example of the situation before and after the preset. If you don't have Color Efex yet, you can find it here download.