To my knowledge, no screenshot is available.
To customize the theme of OCS reports :
1 - Make a copy of the original theme folder :
cp -R /usr/share/ocsinventory-reports/ocsreports/themes/OCS /usr/share/ocsinventory-reports/ocsreports/themes/My_business
Note: "My_business" is the name of your business, activity, etc.
2 - Go to the "My_business" folder and replace the 2 images with yours, edit the css file and replace the colors with your color chart (note : The top colour of OCS is #961b7e)
3 - Go to OCSreports - Configuration - Interface and at "Custom_theme" change the default theme (OCS) to your theme (for example: "My_business")
4 - Apply, that's all !