Can a person add a dye spot on the middle of a poured egg? I have the egg mold and I know it is almost impossible to add it while injecting but can it be done afterwards?

Also, how would I add a dye spot to the outside of the egg? I think this could be done with a small piece of plastic in the mold before injecting. Would it be best to do it that way or just use a sharpie to add a color spot?