The present invention is related to water-based inks for making colored hydrogel contact lenses, in particular, colored HEMA-based hydrogel contact lenses. The ink of the invention comprises at least one colorant, water, and a water-soluble and actinically-curable binder polymer which is a vinyl group-terminated polyurethane polymer, a vinyl group-terminated polyurea binder polymer, or a mixture thereof. Also, the ink of the invention is characterized by having a viscosity greater than 50 centipoise (cps), a prolonged stability, and a good adhesion to a HEMA-based hydrogel contact lens. The ink of the invention preferably further has a good compatibility with a HEMA-based hydrogel material, and/or good transferability from a mold to a HEMA-based hydrogel contact lens made in the mold. The present invention is also related to a method for making colored hydrogel contact lenses using an ink of the invention.