(RGB is the same way sRGB values produce a different color than Adobe RGB values, and if someone tells you no RGB color space was used, that just means an RGB color space was assumed but they don’t realize it.) For example, putting US Web Coated SWOP values through a different process (such as sheet fed uncoated) will get you slightly different colors. Using CMYK numbers always assumes a specific CMYK, because the numbers only get you the color you expect when the values are applied to a specific set of process color inks. The print shop wants me to not use any flavor of CMYK.
