Press the 'advance style settings' button to expand the settings section, make your changes, then click the 'update style' button towards the top of the page (under the big image). Make sure the colour is set to Custom (select below).
If you update the style, you'll need to refresh the page before you can make further changes.
Comments
If you update the style, you'll need to refresh the page before you can make further changes.
If this doesn't work, let me know.