Well, to be blunt, don't do it. One puppy at a time is plenty. There is some thought that a good breeder would not sell you two puppies at the same time or sell you one if they knew you had another the same age. I don't know about that but I know it will be a whole lotta puppy!
I also think it a misconception that you expect to choose two pups the same age and of different coloring. I don't fault you for this as I'm sure I thought the same way a few years back. A good breeder often chooses the dog that will work in your household. But this sounds a bit like you are picking out matching cars in different colors. It just doesn't work that way in my experience.