Yeah, it's for printing since the standard ink colors are cyan, magenta, yellow, and black. (The K stands for "key" and refers to the black ink but idk why it's called that..)
When you're designing or illustrating something for printed media you need to keep in mind that very bright colors will get dulled. Greens and cyans can get much brighter digitally than with ink. A lot of programs will have a CMYK proofing mode where it attempts to keep the colors in a more accurate range which is what you're describing. I don't make printed media so I don't work with it, but I've heard that photoshop's CMYK mode isn't very accurate and makes the canvas too washed out.
- image.png (154.54 KiB) Viewed 21 times
This is how krita handles the CMYK *space*, which both attempts to limit the color gamut to an ink-based range, and also stores the 4 color channel values per pixel. (I say *space* because you can also use CMYK for softproofing, which only changes the way the canvas is displayed to you and the pixels still keep their original RGB values).
One interesting thing with it is since blackness is it's own color channel, a pixel can appear to be pure black but also be pure yellow/cyan etc. The circles on top were all "black", and I applied a white gradient on top to reveal their color.
In the 2nd row I was seeing how mixing the primaries looks, and on the bottom two I'm mixing the primaries on top of key black, and then 100% black (every channel is maxed out). Overall this space looks pretty ugly in Krita. I wouldn't use this for digital illustration, but maybe it's good for something else. Again, I don't print, so I have no idea if this would be useful for that or not, or if it would just be better to use the CMYK softproofer.
