You add white coloring to all of your icing or just to the icing that will be white? I've never had any bleeding problems when I use white dye, but if you're adding it to the orange, aside from seeming unnecessary (and expensive), you'll have to add more orange coloring to achieve a vibrant color. Maybe that's why it's bleeding (if I'm understanding your process). Either way, you could try dying your icing a couple hours in advance so that you need as little color as possible. That's what I do when I'm worried about bleeding.