RGB versus CMYK colour spectrum:

Another reason to hire a professional to do design work on your behalf is to ensure the colours that are sent to you electronically are accurate when printed. It is essential to understand the difference in RGB (red, green, blue) gamut vs. CMYK (cyan, magenta, yellow, black) gamut and how their ranges could impact your printed design.

Even though all colours in the visible spectrum are merged from red, green, and blue, monitors are capable of displaying only a limited gamut (i.e., range) of the visible spectrum. Monitors emit light, and inked paper absorbs/reflects specific wavelengths. Cyan, magenta and yellow pigments serve as filters, subtracting varying degrees of red, green and blue from white light to produce a selective gamut of spectral colors. Like monitors, printing inks also produce a color gamut that is only a subset of the visible spectrum, but the range is not equal. Consequently, the same art displayed on a computer monitor may not match to that printed in a publication. colours

If you look at the chart on the right, you will notice that RGB colour gamut is a subset of the visible colour spectrum. You will also see that the CMYK gamet is a subset of RGB. All colours outside of the CMYK set can't be printed but you will see them on the monitor because they still part of the RGB gamut.

By understanding the principles behind the colour gamuts, you can ensure that your poster, design, or even printable material from your site is printed as accurately as possible.