Rather than trying to tint the epoxy get a quart of sealer number 7 shade (it's black) and seal the epoxy instead. I wouldn't recommend trying to topcoat over epoxy primer as It's use isn't designed for that purpose. Check your manufacturers spec sheet.
As for mixing the epoxy throughly, yes. All ingredients should be throughly mixed and distributed before applying or your going to have adhesion problems if fail to do so.