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This is very important because any oils will prevent the paint from sticking. It will also get rid of any sanding dust if you trimmed the hook down. Simply soak a cotton ball in rubbing alcohol, then wipe down the outside surface.  You should do this even if you just took the hook out of the packaging. You don't need to wipe down the back of the hook because you won't be painting it. If you paint the entire hook to match your wall, then the actual hooked part will show up against the curtain rod. Masking the hooked part off will leave the original color behind, and help it blend into the rod. Tear off a piece of making tape, then wrap it around the hooked part of your Command hook. Stop when you reach the rectangle or oval that the hook is attached to. You can use the brush-on or spray-on kind of primer. If you are using the spray-on kind, be sure to work in a well-ventilated area and to cover your work surface with a sheet of newspaper. Shake the can before using it, and hold it several inches/centimeters away from the surface. Let the paint dry before moving on. Make sure that you use a primer made for plastic surfaces. If the primer doesn't stick, then the paint won't stick either. You can use spray paint for this, but it would be easier to color-match the hook to your wall with interior wall paint. Use a small brush to apply the paint in neat, overlapping rows. Let the paint dry, then add a second layer if it is thin or streaky.  If you are working with spray paint, be sure to paint on top of a sheet of newspaper in a well-ventilated area.  Use a sweeping side-to-side motion. If you live in a rental unit, ask your landlord for some spare paint. Apply the paint with a brush. Make sure that you pull the tape straight up and away from the hook. Do not drag it across the painted part of the hook, otherwise you risk chipping the paint. If you get some chips in the paint, fill them in using a small pointed brush and some spare paint. Whether or not the paint needs curing depends on the type of paint that you are using. Most spray paints are ready to use after they finish drying, which should only take 15 to 20 minutes. Many interior wall paints, however, have a curing time in addition to a drying time. Check the label on your can of paint. Don't use the hooks if the paint feels tacky. It has not cured yet. If you use the hooks before the paint finishes curing, it may peel off. Once the paint has dried and cured, the hooks are ready to use. There is no need to seal them because they are not being heavily used. In fact, sealing the hooks may mar any metallic finishes. The base of the completed hook will match your wall, and the hooked part will match your curtain rod.

Summary:
Wipe the hook down with rubbing alcohol. Wrap painter's tape around the hooked part. Paint the hook with paint primer intended for plastic surfaces. Paint the hook a color that matches your wall. Peel off the tape once the paint dries. Allow the paint to cure, if needed. Use the hooks.