You can always customize your app as per the requirement - any background/color/font whatever.
Mostly the work - creating dashboard/alerts/reports are done in apps. Best practice is to use custom apps for diff requirement and you can do whatever you want to do in Custom apps.
everything is splunk is configurable (including the UI). I have done it in the past but i cannot remember the instructions. Search this forum for customizing the interface. It will boil down to custom xmls.