Use paint that is compatible with the brick and the location or area where it will be used. Bricks have a flat, matte finish that accepts paint well; choose a paint that dries to a flat finish to closely mimic the look of real brick. If the brick is already outdoors or will be used outdoors, a paint formulated for exterior use will help your project withstand all types of weather. Either flat craft paint or latex paint can be used for this project, depending on the number of bricks you need to paint.
Every batch of bricks is different, so choose your colors based on your existing bricks. For best results, you'll need to select two reds, one that is deeper or darker than your brick and one that is lighter. You'll also need a small amount of black and a light grey or white. Choose colors that go well with your existing brick, and don't be afraid to experiment if you are unsure. A natural sea sponge will add variety to your bricks without making a repeat or distracting pattern, and you can use an old toothbrush to flick random bits of paint onto your brick, enhancing the effect.
Pour the dark red paint onto a disposable plate or paint pan, then dip the sponge into the paint. Dab the sponge into the paint and then onto the brick. Don't cover the brick completely, allow some of the original brick to show through. Repeat, using the sponge and the light red paint. After the reds have dried, flick paint onto the brick using the toothbrush. Dip the bristles into the black paint and run your finger across the brush, releasing a spray of paint to add color and texture to the brick. Let the black dry, and repeat, spattering the bricks with light grey or white.
If your bricks already are installed, tape off any wall or trim that you don't want to paint. Use a dropcloth when you paint the bricks -- the spatter technique gives a realistic finish but is very messy. Once your bricks have dried, they require little care; the paint will be permanently affixed to the surface. The finished bricks can be used anywhere regular, unpainted bricks are used.