Go to the admin console -> permissions tab -> Space permissions -> enter space name -> add group
Assuming you only want your colleagues to have access to this space, then you will need to create a permissions group through the admin console and add your colleagues as members, otherwise, add the group called All Registered Users.
To create permissions group, go to admin console -> People tab -> create group -> enter name and create group -> group summary -> edit group -> edit members -> add colleagues. You can build a plugin that listens for new users created in the Community and are automatically inserted in this group for colleagues whose emails match a particular pattern, such as @abc.com.
Hope that helps!