Flaws and rough patches on the ceiling after painting will only draw the eye to area, further accenting the sloped ceiling. Dust or vacuum the entire ceiling before you begin to paint to eliminate debris that would prevent paint from going on the ceiling smoothly. Some flaws may be in the ceiling construction, such as a rough patch of drywall or an old ceiling texture that's breaking down. Sand smooth rough patches with fine-grit sandpaper. Remove degrading texture features, such as a popcorn ceiling, prior to painting.
Color helps to camouflage a slope when used correctly. Using the same color of paint on the ceiling that is on the walls tricks the eye so the line where the wall ends and ceiling begins isn't as obvious. To make the ceiling look higher and make a room look bigger, select a paint one color, or shade, lighter than the paint that is on the walls. Dark or contrasting colors only make a slope more obvious. Dark colors also can make a space feel small, especially in small rooms and rooms without a lot of natural light.
Paint has a matte, gloss or semigloss finish. A matte finish is flat with no shine, and it does little to disguise a slope. The high shine of gloss and moderate shine of a semigloss paint reflect light, helping a room look more spacious and creating the illusion of higher ceilings. The light reflection helps to camouflage a slope best when it is used in a light-colored paint. The slope is even more difficult to detect if sunlight from a window or artificial light reflects off the gloss or semigloss paint on the slope.
Applying a coat of primer before painting the ceiling in the desired color is helpful. Primer provides a base that ensures the final paint coat goes on evenly, which is vital because flaws will draw the eye to the slope. Primer is especially necessary when painting over a color with a lighter color. Avoid using wall borders and ceiling molding because they also make a sloped ceiling more obvious than it is otherwise. Ceiling-mounted lights and fan fixtures also draw attention to a sloped ceiling.