An Ink-jet ink composition for piezoelectric in-jet printing comprising: (a) a hydrophobic dye; (b) an oil-in-water microemulsion including: (i) a volatile oil; (ii) water; (iii) a co-solvent; (iv) at least one surfactant; and (v) a binder, wherein upon application of the ink to a substrate surface, the volatile oil evaporates and nanoparticles are formed. The invention additionally discloses a printing process using the ink composition.