Due to the complex nature of CMYK printing, all full colour printing is subject to a small degree of colour variance. This means that some colours may look slightly different between one print run and the next. Offset presses reproduce colour more consistently than digital presses but the mixing of inks means there will always be a slight colour difference. This is a common and expected outcome of CMYK printing.
4c/4c, means both front and back sides of the paper will be printed full colour (CMYK).
4c/1c, means the front side will be printed full colour with all 4 colour inks (CMYK) and the back side only receives one ink colour (black).
4c/0c, means the front side will be printed full colour with all 4 colour inks (CMYK) and the back side has no ink and will be completely blank.
Please note: If you want to print you artwork in grayscale (using black only), please make sure to convert any images to grayscale mode in Photoshop prior to using them in Illustrator or InDesign. On screen the image may look black & white, however, unless the image says grayscale mode at the very top, chances are it is not grayscale. Failure to convert images to grayscale may result in the images printing differently than you expect.