1. Design the wall. Decide which three colors you’ll use for the tricolor wall and how you’ll use them. Two colors will be on the wall; one color will be for accessories. (The other three walls in the room should be painted one of these three colors. If they aren’t already, paint them first.)
2. Prep, prime, and tape. Position the drop cloths. Prep, and prime the wall (if you didn’t in step 1). Let dry. Apply the painter’s masking tape to the ceiling and baseboard, as well as to the flanking walls (except in places where the color will not change from wall to wall). Press the tape down firmly on the edges that face the wall that will be painted.
3. Paint the top of the wall. With the pencil, mark a rough line on the two-color wall a little below where you want the colors to change. With the brush, paint a band about 2 inches wide at the top of the wall. Pour some paint into the tray. Use the roller to paint the rest of the top section of the wall, painting a little below the rough color-change line. Remove the tape at the ceiling and sides of the upper part of the wall. Wipe off any paint that seeped under the tape. Let dry.
4. Establish the color-change line. Use the carpenter’s level and a pencil to mark a horizontal line precisely where the colors will change. Apply tape on the newly painted surface just above that line. Press the tape down firmly on the edges that face the unpainted portion of the wall.
5. Paint the bottom of the wall. Using the same procedure you used in step 3, paint the lower part of the wall with the second paint color. Remove the existing tape. If any paint seeped under the tape, wipe it off. Let dry.
6. Add the third color. Use the third color to paint a shelf that will hang on the duotone wall (as pictured here), the trim, or a chair or a bookcase that will sit near or against the wall.
Right after step 4, brush a little of the top color paint along the edge of the tape that faces the bottom portion of the wall, and let it dry. The paint will seep into any gaps and plug them, leaving no room for the second color to sneak in there when you paint the bottom portion of the wall.
The palette pictured here is called Cascada; it consists of peacock blue, cool slate, and pale gray.