We don't currently have the ability to print metallics, foils, or white inks on our boxes.
We use digital printing processes, so all of the color is created using CMYK (Cyan, Magenta, Yellow, and blacK) inks. We cannot print in white or metallic inks. If you have areas in your design that are "white," those are areas that will not be printed. So the color of the box material you've chosen (Kraft brown or white) will show through to create the design effect in those places.
However, it's something we are considering for the future, so stay tuned to our product offerings to be among the first to know when it's available! :D