If you are giving us vector artwork, please change your colors to CMYK and convert any text to curves.
We prefer .eps files as these keep most of the information about a vector.
Suppose you want clear, holographic, fluorescent stickers or your design printed on any color other than white material. In that case, we'll probably need to add white ink where you want 'normal' colors in your design.
If you don't put white ink behind a color, the vinyl will partly show through, giving your color a metallic or transparent effect.
Below you will find a useful video about how to add a cutline and white layer: