Leave that the same as LR

Is there a wooden door facing on this opening? If so, it's easy, the door facing is trim, so it's painted with the trim color, which it see is white. If there isn't a facing, add one.

All of the living room should be the same color.

Same color as livingroom. The cream color.

Great question. When you transition paint color from on room to another and there is a strong contrast between colors it gets tricky. In viewing the images submitted your strong color should have stayed in your living room only. The top of the header was painted "a color" and it brings attention to it. That should have been white and treated as a ceiling. The reason is, it's less disruptive to visually adjust to the lightest or least contrast color on a 5" wall return. The secret is being discreet in transitioning.

Hope you understand and it helps. Good luck.