This page is using a free Spruce theme, courtesy of Bootswatch.

To use this theme with Reflow Maven skin, use the following <theme> configuration in the site.xml site descriptor file:

<custom>
  <reflowSkin>
    ...
    <theme>bootswatch-spruce</theme>
    ...
  </reflowSkin>
</custom>

Find other theme options for Reflow Maven skin here.