CMYK stands for cyan, magenta, yellow and key (black), the four inks most full-color printing presses use. RGB stands for red, green and blue, the three colors of light that phones, monitors and TVs mix. A file made for a screen is usually RGB; a file sent to a printer is usually expected in CMYK.
The two modes do not hold the same range of colors. Bright screen colors, like a glowing lime green or an electric blue, often look duller once they are printed with ink. Converting to CMYK before printing lets you see that change on screen instead of being surprised by the finished job.
Imagine a yoga studio called Still Water Yoga that designs a teal flyer on a laptop. Printed straight from the RGB file, the teal comes back a flatter blue-green. Checking it in CMYK first lets the owner pick a teal that prints the way she wants.
In aiKit, Printer's Helper reports RGB color in a file instead of quietly changing it, Pro Designer Automate converts a whole batch of files to CMYK, and Vectorize Kit lists every logo color in HEX, RGB and CMYK.
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See it in practice
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