Whether it ranges from a pale golden-brown to an almost burnished auburn with hints of yellow, caramel colored frosting requires blending brown and yellow food coloring with white frosting. Because it requires brown -- a dark color -- you may need to tint the frosting before coloring it. Using too much food coloring can give frosting a bitter, off taste. Because caramel colored frosting can vary between pale to very dark, you can use either only food coloring or a mix of food coloring and cocoa powder to color your white frosting.
The type of icing you use affects how deeply you need to color it. Buttercream frosting causes colors to darken and intensify one to two hours after mixing. Royal frosting and boiled frostings, as well as those designed to have a semi-liquid flow, fade slightly after the color has been mixed in. Before mixing the full batch of frosting, use a toothpick dipped into the coloring and mix with a small sample of the frosting. This test checks that your color works well with your icing type.
The easiest way to make caramel-colored frosting is to use a mix of brown and yellow food coloring. If you do not have brown food coloring, combine red and green coloring in a 1-to-1 ratio, for example, 2 drops of red and 2 drops of green for 1-tablespoon of frosting. (personal experience) Caramel is often a light yellow-brown, so you do not need a lot of brown coloring, as the white will help temper its natural intensity. Add only a small amount of yellow coloring to give the frosting a gentle, golden hue. For a medium-dark caramel color, use a 3-to-1 ratio of brown and yellow food coloring, and a 2-to-1 ratio of food coloring to frosting, measuring the coloring in drops and the frosting in tablespoons. This means 2-tablespoons of white frosting needs a total of 4 drops of food coloring -- 3 drops of brown and 1 drop of yellow coloring -- for a medium-dark caramel color. Reduce the number of drops of brown coloring by one for a pale caramel color, and increase the drops by one or two for a darker caramel color. (personal experience)
Natural Caramel Frosting Options
You can also make caramel colored frosting with a mix of cocoa powder, either natural or Dutch process, and food coloring. The cocoa powder gives the icing a deeper, richer flavor, and it also tints the frosting brown, meaning you can use less food coloring. Caramel syrup is generally not used to color white frosting, as the syrup can be used only in small amounts, otherwise it alters the consistency of the frosting. Because of this, caramel syrup adds more flavor than color to frosting. Use a 1-to-1 ratio of cocoa powder to frosting, and then add 1 drop of yellow frosting for every tablespoon of frosting for a pale caramel color. For a darker caramel, add 1 to 2 drops of brown food coloring for every tablespoon of frosting, in addition to the yellow coloring and the cocoa powder. (personal experience)
Caramel- -- or brown- -- colored frostings can develop an unnatural tint when only food coloring is used. Acid in the frosting, such as lemon juice or cream of tartar, may cause brown frosting to develop a green tinge. To prevent this, dissolve the food coloring in a 1/4 teaspoon of water before adding it to the icing, or keep the acid component out of icing that will be tinted brown. If you end up needing to use a lot of pure food coloring to create the caramel color, add a pinch of salt to the icing to temper any bitterness.