Try this trick using acrylic paints:
If you need a brick red and do not have any, it is easier and cheaper to just mix bright red and brown.
Another brick red color suggestion is a mixture of red oxide, black, burnt sienna, cadmium red and white. To do this:
Lay out 1 tbsp. each of the red oxide, black, burnt sienna, cadmium red and white on your mixing surface or palette.
Mix about 1 tsp. of the black into the white. Smear it about with the palette knife. The flexible blade of the knife makes it easier to blend acrylic colors than if you employed regular knife or spatula. Mix until you have an even gray.
Mix 1 tsp. of your gray hue into the red oxide. Again, blend well.
Review your color. If you have the brick color desired, stop. If not, you must adjust it.
Add 1 tsp. of cadmium red for a more brilliant red brick. Add 1 tsp. of burnt sienna for an earthier color. Add more gray for a neutral red, one that looks less colorful. Add a tiny speck of black to darken the brick hue.
Having knowledge of the color wheel, along with an understanding of the difference between primary, secondary, and tertiary colors will make your color-mixing a lot easier, as will a grasp of complementary, warm and cool colors.
Check out some tips on how to mix colors when painting at Visual-arts-cork.com.