I agree with a few opinions here on the color.
It's been a while scince I was in the Ad game, but if I remember correctly, 4 color is different from CMYK in the print process and approach.
4 color is 4 separate passes with 100% saturation. The actual colors are irrelivant. You get a color pallet from the printer, and pick 4 that you need and use them in your artwork. They hit the media (bag, paper whatever) like paint. NO shading or gradients.
CMYK is mixing of the 4 colors to give accurate color reproduction, including gradients shades. Cyan, Magenta, Yellow and Black are mixed at different percentages to achive more realistic color reproduction.
Of course with DIgital printers these days, who know hat you can get in short run.
Anyone here work at a print house? Am I remembering correctly?