Color image forming method and apparatus providing for efficient toner transfer based on toner zeta potentials

An electrophotographic color image forming apparatus comprising:

• a plurality of liquid developing devices, each accommodating a liquid developer that comprises a colored toner dispersed in an electrically insulating carrier fluid;
• wherein said liquid developing devices sequentially form toner images of different colors on a transfer medium via an electrostatic transfer, each of said toner images after a first of the toner images and up to a last of the toner images being superimposed over a previous of the toner images to produce a multilayer toner image;
• and
• wherein each liquid developing device sets the absolute value of the zeta potential of its respective liquid developer, such that the absolute values of the zeta potentials are set sequentially increasing from the liquid developing device that transfers the first toner image to the liquid developing device that transfers the last toner image to improve efficiency of the toner transfer.