1/2 cup water 1tbsp cornstarch 1 (or 1/2) egg white A little bit (~tsp) of something white. Sour cream, yogurt, nondairy creamer, whatever)

Dissolve corn starch in a little bit of water, then add the rest. Bring to a simmer until it thickens, then let it cool down. Once cool, add egg white and color.