I've setup an "editor1" user that has permissions to add and edit Page content.

But the interface they see in editing is a tad uglier than my admin login and image thumbnails appears corrupted.

Example - Here is the EDIT "About us" page for my admin user:

 

and here is same editing view for the Editor1 user:

 

Does anyone know what I can do to change the Editor1's appearance to match the admin one?

 

Accepted answer

Give the Editor permission to "View the administration theme" on the permissions page:

admin/config/people/permissions

As admin your admin experience is controlled by the admin theme instead of your regular theme. Your site editor will not have access to this admin theme unless you give it to them. 

 

Comments

Give the Editor permission to "View the administration theme" on the permissions page:

admin/config/people/permissions

As admin your admin experience is controlled by the admin theme instead of your regular theme. Your site editor will not have access to this admin theme unless you give it to them. 

 

ah yes perfect, thanks for that!