How do you add food coloring to sponge cake?

To add food coloring to sponge cake, add small amounts (about 1/4 teaspoon) at a time to the batter and mix well until you reach your desired shade.

Here's a more detailed breakdown:

Steps for Adding Food Coloring to Sponge Cake Batter:

Prepare your sponge cake batter according to your recipe. Make sure it's fully mixed and ready for coloring.
Divide the batter (if needed). If you want multiple colors, divide the batter into separate bowls. The number of bowls depends on how many colors you want.
Add food coloring gradually. Start by adding just a small amount of food coloring (about 1/4 teaspoon) to one bowl of batter. It’s always easier to add more color than to remove it.
Mix thoroughly. Gently fold the food coloring into the batter until it's evenly distributed and you achieve a consistent color throughout. Avoid overmixing, as this can toughen the sponge cake.
Assess the color. Evaluate the color in good lighting. If it's not the shade you want, add another small amount of food coloring and mix again. Repeat until you achieve the desired color.
Repeat for other colors (if using). Follow steps 3-5 for each bowl of batter with different colors.
Pour into prepared pan(s). Once all batters are colored, gently pour them into your prepared cake pan(s). If creating a layered look, carefully spread each color to level.
Bake as directed. Bake the sponge cake according to your recipe's instructions. Baking times may vary depending on the recipe and oven. Check for doneness with a toothpick – it should come out clean when inserted into the center.

Use gel food coloring. Gel colors are more concentrated than liquid food coloring, so you'll need less to achieve vibrant colors. They also won't change the consistency of the batter as much as liquid colors.
Mix gently. Overmixing the batter after adding the food coloring can develop the gluten and result in a tougher cake.
Test the color. For accuracy, bake a small test portion of the batter to check the final baked color. Colors can sometimes change slightly during baking.
Be patient. It's better to add the food coloring gradually to avoid over-coloring the batter.
Consider the oven temperature. High oven temperatures can sometimes cause colors to fade slightly during baking.