How to paint rooms in my house different colors?

You can paint the walls right up to the corners, and then use a piece of corner molding to cover the corner and create a small break between the colors. It adds a bit of interest as well.

With the curve in bull-nosed corners, I'd snap a chalk line down the center of the corner, then apply painter's tape along one side of the chalk line. Paint, remove the tape, then put the tape on the painted side (after the paint has dried a day), then paint the other color.

I agree with Sal85902. My brother did this and we used painters tape in the corner and it worked beautifully. The finished project was great and it was an easy and cheap way to work around the cove or bull nose corners.

You may consider the method descibed, with the tape at the end of the flat surface, before the curve.... but this depends on your room layout and your viewpoint(s) as you use the space. Sometimes it's best to make the Other color Not visible, so the middle of the bullnose may be too much a compromise.

This may also create too much 'debate' about how to handle the project.

If you have rooms that flow into each other and you paint them different colors you may end up with your home looking a little chopped up. Painting just one color will unify the space and then you can differentiate the areas with things like rugs, pillows drapes, etc. When you have rooms that are open to each other its a good idea to take colors from each room and used them in the others - a little cross pollination of color.