1. An image forming method comprising: by using a plurality of liquid developers having different colors, forming a plurality of single color images corresponding to the colors; transferring a non-fixed color image onto a recording medium; and fixing the non-fixed color image onto the recording medium, wherein said fixing uses a fixing device that comprises a thermal fixing roller and a presser roller, wherein each of the liquid developers includes an insulating liquid containing unsaturated fatty acid components, a saturated fatty acid component, and a fatty acid monoester and toner particles dispersed in the insulating liquid, and an oxidation polymerization accelerator that accelerates an oxidation polymerization reaction of the unsaturated fatty acid components during fixation is contained in the liquid developer forming the single color image that is positioned closest to the recording medium among the plurality of single color images forming the non-fixed color image, wherein the oxidation polymerization accelerator is contained in only the liquid developer forming the single color image that is positioned closest to the recording medium among the plurality of single color images forming the non-fixed color image.