I think your floor looks great!!!! But everyone has their own idea. I'm not sure you can add color to a urethane topcoat layer as normally the color is in the epoxy coat.
With the polyurea products however you can add color. You might talk to one of the single part polyurea folks (eg. allgaragefloors and I think armorpoxy has a single part polyurea as well and see if applying that over a urethane top coat is feasible. You would be doing two coats first with polyurea with a color additive and a second clear coat.
Otherwise I think you are down to grinding the entire floor out and starting over. That said I think your floor looks gorgeous as is.
For what it is worth, I did an Armorpoxy ultra with light grey about 3 years ago. And was unsatisfied with the yellowing that occurred. It wasn't necessarily Armorpoxy, rather epoxy is UV sensitive. I've recently moved and this time around am going with the one part polyurea. The older polyaspartic and polyurea products were too difficult to apply as the working times were difficult, but these new one part products are pretty much ideal.. Long pot times, quick curing and not subject to inherent epoxy yellowing. (and yes it yellows around the edges even if you don't leave the garage door open)
I also didn't really care for the jumbled armorpoxy site. I think the product was decent (other than epoxy yellows) But figuring out what products they have and what combinations was really confusing and difficult for someone who likes to research on their own without talking to a sales guy. They seem to market the same products in different combinations and call them different things and was just too confusing to figure out what I was getting. I was never really satisfied with the terse responses I got to basic questions when trying to sort out which products where which. Also couldn't stand all the "military" BS hype.. Nothing but nonsensical marketing. There is no such thing as "military" grade so it tends to degrade my trust and feel like it is a shamwow experience.
Good luck.