What is a color toner?

Toner is a powder used in laser printers and photocopiers to form the printed text and images on the paper. In its early form it was simply carbon powder. Then, to improve the quality of the printout, the carbon was melt-mixed with a polymer.Toner particles are melted by the heat of the fuser, and bind to the paper.

In earlier machines, toner was poured by the user from a bottle into a reservoir in the machine. Modern machines feed directly from a cartridge. Empty cartridges are sometimes refilled by third party vendors.

Modern toners intended for use in color copiers and printers come in Cyan, Magenta, Yellow and Black (CMYK).

Source: Wikipedia