Blending 2 room colors - rounded corners

[DD716TED]

I have two rooms that are connected by a door and a ceiling opening that both feature rounded corners. If the opening and door had square edges it would be easy to paint each room a different color, however since they are all rounded, I am looking for ideas and suggestions on how the blend or break the color lines between the rooms.

[LazyPup]

In the room you make a vertical line where the radius of the curve meets the flat wall. The color on the radius will then give the optical illusion of a trim molding on the door and would be less noticeable.