Hi Praneeth. A red highlight on an association in the Domain Model means that the association has delete rules on it. You can double click the association to view these details.

To further the correct explanation of Edgar Gutierrez with a practical example: say you have a “Customer” entity, and an “Order” entity. They’ll normally have a 1-* relationship, and should always be higlighted, since you never want a Customer entity to be deleted, just because his Order was deleted, but you want all orders of a certain Customer to be deleted when that Customer got deleted. If you would put both “on delete” rules back to “Keep ‘Customer’/’Order’ object(s)”, the red highlight would disappear.