Cyan Magenta Yellow Black is the base four-color process used for most printers.
Technically, adding equal amounts of pure cyan, magenta, and yellow should produce black. However, because of impurities in the inks, rich black is not achievable using just Cyan, Magenta, and Yellow. Using the three colors is costly, and additionally puts too much ink on the page.
CMYK is a smaller color gamut than RGB, l*a*b*, or others. Before converting any image or graphic to CMYK, first, save the file and tag it with the original color gamut. Append the name of the record with CMYK.
Gamut is referred to as a range, also referred to as a color space. Color is presented in a 3D shape, and the gamut is the range of colors achievable in that color space. A color gamut relies on three factors, colorant, material, and technology. With all three, a creative can specify color with accuracy and confidence. If a gamut is chosen, simply on one of three, then color shifts will occur due to limitations or characteristics of material and technology.
Red, Green, and Blue is a color space typically used for digital screens, TVs, and tablets.
RGB is referred to as additive colors, where colors begin as black, darkness, and shift to create white. Screens have hundreds of thousands of pixels. Each pixel has three sub-pixels: a red light, green light, and blue light. These sub-pixels light up in different intensities based on the color the pixel ultimately displays to produce a result on a black monitor. By superimposing red, green, and blue light, a large array of colors can be created.
RGB will give the perception of brighter colors, when compared to physical colors, like print and packaging. RGB color space is significantly larger than CMYK. When converting an image from RGB to CMYK, the software is 'amputating' the color space. If you need to work in multiple color spaces, it is best to save the file in each color space.
The RGB value for black is: R: 0 G: 0 B: 0
The RGB value for white is: R: 255 G: 255 B: 255
When saving a file, it is best to amend the file name with the color space.