You can customize the look of the 7Zip Archiver with the help of an application called 7Zip Theme Manager.
This application is available for downloading from the following website: http://www.7ztm.de/index.php?cat=01_English
To apply a theme, download and install the application, then start it. The software will automatically detect the 7Zip installation and provide additional warnings if there are any.
Use the image below as guidance: