Place egg whites and lemon juice in the bowl of an electric mixer with the whisk attachment. Beat on high until peaks form.
Heat honey in a small saucepan over medium-high heat until a candy thermometer reads 240F or the honey begins to bubble and froth.
With the mixer still on high speed slowly pour the honey into the whipped egg whites. Continue beating on high until the mixture is at room temperature, about 20 minutes.
Reduce mixer speed to medium and add the butter 1 tablespoon at a time. Add the vanilla extract and spinach juice or food coloring. (If the frosting is runny simply place in the refrigerator until chilled and beat again.) Makes 3 cups of frosting.