How additive and subtractive colour works when printing a digital image
When you create a digital image and then print it on paper, this involves a process of converting the additive colour system (RGB colour) in your digital image to a subtractive system (CMYK colour inks) that prints the correct colours onto paper.
Your image editing software or printer software is going through this conversion process, attempting to match what we can see on the digital screen with what will come out of the printer. It’s a complex process, and there are many different automated and manual methods for colour conversion.
More detailed information about subtractive colour and the print process can be found in 3.3 Colour systems: printing. View this page for more about converting images from RGB to CMYK.