Of all the millions of colors that the eye can see, your printer can only print a very small subset of them. That subset is called a "color space".

If you are trying to print a "Cardinal Red" (a popular vinyl color), you will not be able to. That color red is outside the color space, or color gamut, of most CMYK printers. TO get that Cardinal Red, pigments are specifically found and "poured" into the vinyl to produce that specific color of red.

That is why we have provided the CMYK swatch chart for you to use. Those are the colors inside of the color space your printer is capable of printing.

You can read about that here in our blog article linked below.
Basic Guide to Color Space 

Be sure also, to watch our informative "Match By Output video tutorial. It explains some of the same limitations and offers a better color management tool". 

I hope the above information is helpful.