Use black gel food coloring and add it directly to frosting, batter, or icing
Mix equal parts red, blue, and green food coloring until the color turns very dark
Add a small amount of black cocoa powder to deepen the color in baked goods
Use activated charcoal food coloring if it is approved for your recipe and region
Combine dark chocolate, black cocoa, or espresso powder with your mixture for a darker result
Let the color develop for several minutes before adding more
Add color gradually to avoid over-thinning the mixture