The field must be made 'visible' for both User Story and Task work items in the Workspaces & Projects fields configuration settings.
Be sure the VISIBLE item is checked off. When making this change the administrative user will need to log out and back into Agile Central to see the changes in the work items.
After making the above change the column picker in the Custom List app will show Actuals (User Story, Task) as shown here.
The Custom List app displays both User Stories and Tasks (as children) in the app, both of these work items must be configured to be visible in order for the field to display as a column.