1/2 cup nonhydrogenated shortening
1/2 cup nonhydrogenated margarine
3 1/2 cups powdered sugar, sifted if clumpy
1 1/2 teaspoons vanilla extract
1/4 cup plain soy milk or soy creamer

Beat the shortening and margarine together until well combined and fluffy. Add the sugar and beat for about 3 more minutes.
Add the vanilla and soy milk, and beat for another 5 to 7 minutes until fluffy.

I found the above recipe. Earth Balance makes a non-hydrogenated margarine and Shortening,and I would think that you can substitute Rice Milk for the Soy Milk.

As for the food coloring, I found a product online that might be what you are looking for.

So give it a try and let me know. Good Luck!
The Kitchenner Rebbe