Active Reference Overrides Color.
How to activate a Reference and set override color for other Referencesand active model.
When a Reference is activated, only operations on the activated Reference are permitted. By default, the elements in other References and the active model are displayed with an override color.
You can control whether or not an override color is used, and what the color is, with the Active Reference Override Color setting (Workspace > Preferences > Reference category > Active Reference Override Color setting. In addition, the reference is locked so that it cannot be edited in another session.To edit a reference from within the active model, right-click on the Reference in the References dialog box and select Activate from the po-up menu.