Painting - Edge for different color paints on a round corner

I have knock down finish with round corners throughout the house. It is currently one color (bone white) so the corners work. We would like to add some more color to some of the rooms, but that means butting different colors at the center of the corner. We have looked at some model homes and they seem to just run tape down the center of the corner. However, since the corners have knock down finish, the line where the colors meet appears to be jagged. What is your recommendation for joining the colors and getting a smooth straight vertical line at the center of the corner? Or is there some other technique?

What i have found that works the best is using the blue pressure sensitive tape,It is thinner than your standard blue tape.And i would pick one side or the other for your edge never down the center.I usually make it a flow in ,Meaning take the color to the out side outside corner of the room you are working inand when you brush your line brush away from the tape as a added measure to keep paint from getting under your tape,*****************