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 this article, "A basic guide to color space". the link is below.

Be sure also, to watch the video tutorial here that explains some of the same limitations, "Match By Output, a better color management tool". The link is below.
I hope the above information is helpful.