You can change the appearance of the admin panel in the following ways.
Change the admin panel color
To change the overall color of the admin panel, go to [Environment] -> [Admin panel]. Select your color of choice from the dropdown list next to "Admin panel color".
Change the display language
To change the display language of the admin panel, click the globe icon in the upper right corner of the screen and select your language of choice. This change only applies to the admin panel and does not affect the front-end.
The available languages to choose from are Japanese and English.
Add widgets to the dashboard
To add custom widgets, see FAQ: How do I edit the widget at the top of the administration screen?.
Modify the display of the article editor screen
You can modify the editor screen for a content group through the "CSS" field of the content structure editor.
See FAQ: Can I change the content displayed in the article editing screen? for details.