Please keep in mind that there is no white ink in CMYK offset printing (we do offer white ink printing on some products). Any white areas in your design will be left unprinted revealing the stock itself. If you want to express white areas in your design it is best that you select a white stock.
4/0 - Full color front / Blank Backside
4/1 - Full color front / Black ink only on the back (grey that uses CMY values is considered full color and you will need to select 4/4);
4/4- Full color front/ Full color back.
Regardless of how many colors your design has, it is considered as full color for at least one side.