...

body 
{
  background: ${color1};
}

5. Clustered Environments

Be careful as the above approach will not work out of the box for a clustered environment. For example, if server1 and server2 sit behind a loadbalancer and your wicket app is freshly started it might happen, that the first user gets directed to server1, from which he gets the start page. This page may include dynamic css like above which the browser now loads in a separate request which maybe gets delegated to server2, which maybe has never initialized the start page. Now the wicket app from server2 serves the css without resolving the variables.