When it comes to energy levels, the most important attribute tends to be the saturation of the colors. The higher the saturation, the more energetic the color. For example, tans, greys, and pastels all give off a sleepy, soothing feeling whereas bright, primary colors help to add energy to the feeling. Take a look at the three color palettes below.
The first color palette is highly energetic, albeit a little juvenile. This is a very informal color palette, that could easily be used to market a website to children or a fun and free website. Colors at full saturation have the drawback of sometimes causing the feeling of anxiety in adults, as well as sometimes being too high-contrast which can make them harder to read. You'll want to keep this in mind when designing websites that hold a lot of content or text.
The second color palette is what you could call the mid-road between sleepy and energetic. Colors within this palette still stand out, but they blend well together. This palette could easily be used to market any number of websites from a personal blog to a professional restaurant's menu page.
The third palette has a much more relaxing and professional feel. The colors don't contrast highly with each other, making it ideal for a website that is looking to create a soothing feel, such as a website for a spa.