You can tweak the Xbox One Dashboard and interface in a couple of ways to make it truly your own. Go to 'Settings' then 'All Settings' and choose 'Personalization' from the list on the left. You can pick 'My color & Background' from the options and then 'My Color' to change the main color used on the Xbox One interface from the regulation green.
There's also the option to tweak the main Dashboard background in the same menu, either using a custom image you've saved to your console or a screenshot you've taken. You'll need to install the Media Player for this if you don't already have it. If you're using a custom image then you can adjust the transparency of the Dashboard tiles as well.
