In a stand mixer beat egg whites until frothy and incorporate sugar until smooth. Then mix in the rest of the ingredients. When you've reached the consistency you like, add either food coloring or cocoa, little-by-little until the color you desire is achieved. I made this batch twice and added the dark cocoa only to one and pink food coloring to the other.
Advice and pointers:
Because you're using raw egg whites and salmonella is a risk, always use fresh eggs from a reliable source and don't allow unused frosting to sit out for more than an hour or so. Any unused frosting can be covered with a damp towel to prevent drying and retain freshness, and then placed in the refrigerator. Keep in mind the longer you work with a single batch the darker the color will become, so when initially mixing, keep that in mind.