I always use the McCormick bottled food coloring. It comes in a 1-ounce bottle and yes 2 bottles are what you need. It gives that deep rich color and it does not alter or give a bitter taste to the cake. However, there are all kinds of colorings you can try. Gel colorings work well. There are also natural colorings available like beet powder. Feel free to experiment if you would like. I just stick to the basics here.