Repair an ceramic sink / enamel, and have perfect color match
I am very dubious of the possibility of "a perfect repair in terms of color". Perhaps you should be simply asking "How could I tint this epoxy repair paste?".

You can use regular paint pigments to tint 2-part epoxies. Using a flat board as a pallette, stir up some dabs of paste and start adding small amounts of various pigments to each dab. When cured, compare each dab to the surface to be repaired until a close match is found. Keep careful track of dab size and pigment used so you can duplicate for the actual repair.

This is an art, not a science. You might get close right away, or you might go through 20 "test" packages of epoxy and 100 (1000?) dabs of paste before you get it right.