I don't know of any way to do this; never heard of Perma Crete. If the label on Perma Crete says it will work, then go for it. But I have my doubts. Paint on floor tile usually wears off right away, unless you use an epoxy paint.
It sounds like you have a porcelain tile, and that can be a very durable floor. How about changing grout color? You can get grout stains at home centers. Typically you would have to go toward a darker grout.