You can via the Group Policy specify the default theme or visual style for new users who logs on for the first time.

To do so, type gpedit.msc in start search and hit Enter to open the Group Policy Editor.

Navigate to User Configuration > Administrative Templates >  Control Panel > Personalization.

Now in the right pane, double click on Load a specific theme.

A new window will open. Select Enabled and enter the path of the .theme file you’d like to load, in the Options box.

Themes are located in C:\Users\Username\AppData\Local\Microsoft\Windows\Themes\ folder.

Click Apply > OK.

This setting specifies which theme file is applied to the computer the first time a user logs on.

If you enable this setting, the theme that you specify will be applied when a new user logs on for the first time.  This policy does not prevent the user from changing the theme or any of the theme elements such as the desktop background, window color, sounds, or screen saver after the first logon.

If you disable or do not configure this setting, the default theme will be applied at the first logon.

This setting not working for you ? Try this !