Patent ID: 7670417

Claim:
A composite color, comprising: a first colored ink including amphoteric pigment particles either formulated at a basic pH so that a surface of the pigment particles carries a net negative charge or formulated at an acidic pH so that a surface of the pigment particles carries a net positive charge; and a second colored ink including amphoteric pigment particles either formulated at an acidic pH so that a surface of each of the pigment particles carries a net positive charge or formulated at a basic pH so that a surface of the pigment particles carries a net negative charge, the first colored ink exhibiting a color that is different from that exhibited by the second colored ink; each of the first and second colored inks including a molecule having one group capable of being ionized to carry the net negative charge and an other group capable of being ionized to carry the net positive charge; wherein the first colored ink and the second colored ink have opposite charges; and wherein the composite color exhibits enhanced color richness when printed on a substrate.