THE FOUR COLOURS USED BY PRINTERS
There are four colours used by printers - black, cyan, magenta, & yellow. Some printers will offer additional colours e.g. red, green, photo black etc, but of the four colours first mentioned, they can combine to form any other colour.
The black colour can be defined as the absence of all other colours. The reason that something seems to be black to the eye is that no visible colours are reflected back.
Black can be printed by combining 100% of the three other colours, Cyan, Magenta & Yellowcolours (in which case a black cartridge is not needed). In fact with many printers, if your black expires, the colours will automatically take over to print in black, which is an expensive way to print as they normally are far more costly than the black. Also producing black by combining colours has its drawbacks & can create a colour closer to a brown or gray.
Cyan is also called process blue and is one of the subtractive primary colours used in the C,MY9K) colour model. The Cyan colour is predominantly blue with some green in it.
Magenta is also called process red and like Cyan is one of the subtractive colours used. The magenta colour is greenless and is predominantly redwith some blue in it.
Yellow is one of the subtractive primary colours used in the CMY, and CMYK colour models. The yellow colour is blueless meaning that it absorbs all wavelengths of blue from light.
The cyan, magenta , and yellow individually are normally inserted as a cartidege into the printer, or as a combined cartridge of cyan, magenta & yellow. They never form a combination with the black.