To dye in two or more colors, pink and blue for instance, separate your beaten egg white batter into two different bowls, add a single food coloring to each (one or two drops at most), and when you're ready to bake, gently, and with a minimum of effort , fold the two together with only one or two swirls to give a marble effect, yet not muddle the two colors together. Carefully and slowly pour into your cake pan without any more stirring. Bake.
DON'T try pouring them separately and then folding after they are in the baking pan. Always do that while still in a mixing bowl in order to get a nice swirl effect.
"Food is our common ground, a universal experience." - James Beard