The New function on the Report Themes form allows you to create your own custom Report Themes
These themes are automatically saved to your SI Server and are available to all users.
These themes are user and machine specific so if you want to share these with other users of SI 2017 you will need to manually copy the folder (folder is named whatever you named your Theme) from your machine to their machine. Themes are in the following folder: C:\Users\username\AppData\Roaming\D-Tools\SIX\Data\Reports\Themes