I'm currently designing a mockup for print but unfortunately the logo extends some colors that are only available in RGB.
I was trying to convert a pretty agressive RGB green (#afff00) to CMYK but the differences after the conversion via photoshop are capital.
If I'm printing the RGB logo I get a color thats very very close to the RGB one on the monitor, how is that possible? Is it possible to use that or a pretty similar color in CMYK?
When you send anything to print that is in the RGB color space, the printer driver will ultimately need to convert your document to CYMK to tell the printer how much Cyan, Yellow, Magenta, and Black ink to lay down on the page.
Therefore due to variances in how different printer models (and therefore drivers) make this conversion, it's impossible to know how colors will look once printed if the printer is given color information not in the CMYK space. For instance, a printer with only 4 colors might interpret a bright green in one way, but a printer with 6 or 8 colors might produce a much more different looking result. Some very high end printers night even have dedicated Red Green and Blue inks to mitigate this color space problem, and provide more color gamut when printing from RGB files.
With all of that in mind, when you convert from RGB to CMYK it's not uncommon to see a drop in brightness and vibrance of color as programs like Photoshop want to ensure more consistent results across different printers models due the more limited gamut of the CMYK color space. If color vibrancy is something you're interested in achieving, you should consult with your printer to determine how to best reproduce certain colors. Some printers also make use of the Pantone Matching System (PMS) to ensure correct color results. You can find Pantone swatches in both Photoshop and Illustrator that are designed for accurate color reproduction in the CMYK space.
Certain colors, especially vibrant ones (violetes, oranges and greens), will not look good when converted to CMYK. The reason for that is the fact that when combining red, green and blue in a digital space, you can get a much wider color combination than with analogue printing process of combining cyan, magenta, yellow and black.
How larger RGB color space is than CMYK you can easily see on a diagram bellow (CMYK is shown inside the purple lines). Everything outside that space will be showh with the colors from within the CMYK color space (you can slightly improve the results by changing the rendering intent): https://upload.wikimedia.org/wikipedia/commons/1/1e/CIE1931xy_gamut_comparison.svg
So, to get the best results, make sure you`re converting to a correct color space, because that can increase the gamut if chosen correctly (Fogra 39 for Europe and SWOP v2 for USA are most common ones).
For best results when printing a logo, choose a Pantone color from PMS color chart.
If you do not have a possibility of working with Pantone, you can make conversion situation a little better by removing colors from unnecessary channels - for example, if you have a bright green, thy removing magenta or adding it`s information to another channel in channel mixer, it will look brighter.
