Colors of the color theme are cached on the browser even when the color theme document is updated

How to reproduce:

• Install xwiki
• go to the administration
• customize the already set color theme - the IcebergTheme
  • a visible change is heading color
• save
• navigate to the homepage - without forcing the refresh of browser ressources

Expected result

• the change is visible , headings are colored differently

Actual result:

• the change is not visible, the headings don't receive the different color until the browser cache is force refreshed (shift + f5 on chrome, ctrl + F5 on firefox)