I suggest if you want to experiment, do it on a small piece of concrete and not on a whole garage floor. If you mess up the small piece of concrete, it's not a big deal. If you screw up a whole garage floor, somebody is going to be highly agitated.
also... food dye being edible, will that not have things in there to attract mould, organic growth, pests etc ? I think a lot of them has sugar an alchol