Food coloring comes in three basic forms: liquid, gel and powder. Liquid food coloring comes in bottles that you mix in one drop at a time. Color options are usually limited with the liquid, so you must mix colors to achieve the desired shade of dark orange. The main disadvantage to liquid food coloring is that it can thin out the frosting, so you must make thicker frosting from the start. Gel and powdered food coloring are concentrated, so it takes much less food coloring to achieve dark orange without thinning out the frosting. Additionally, gel and powdered food coloring are easier to find in a wider variety of colors, so you can usually purchase dark orange food coloring without mixing other colors.

Orange frosting is made by mixing red and yellow food coloring. Start with equal parts of red and yellow food coloring. Mix the frosting thoroughly to ensure the colors are evenly distributed. Depending on the exact shade desired, you can use a ratio of two drops of red food coloring for every one drop of yellow food coloring or up to three drops of red to one drop of yellow. If you purchase orange gel food coloring, dip a toothpick in the gel and swirl it in the frosting. Mix the frosting thoroughly and add more until you achieve the desired shade. If it's not dark enough, add a bit of red gel food coloring to make the orange darker. You can shake powdered food coloring into the frosting.

Make a rust color by adding a bit of brown food coloring to dark orange frosting. You can purchase brown gel food coloring and simply add a drop with a toothpick. Liquid food coloring is often limited to red, yellow, green and blue. Red, yellow and blue food coloring create brown when mixed, so you only need to add blue food coloring to the dark orange frosting. Add one drop of blue food coloring and mix it in thoroughly to check the shade. Add more blue food coloring, one drop at a time until you achieve the desired shade.

Frosting colors intensify in buttercream frosting after mixing. A shade of orange might darken two to three shades darker than its shade immediately after mixing. If you add too much food coloring and the shade is too dark, stir in more frosting to lighten the color. To keep the frosting from becoming too dark to begin with, stop adding food coloring when you achieve a shade about two shades lighter than the color that you want. Cover the frosting and place it in the refrigerator for one to two hours while the color intensifies. Check the frosting color after the resting period and mix in more food coloring, if needed.