When we poured ours we added in the charcoal stain with the mix. They still didn't look too dark when dry. I sealed mine with 100% pure Tung Oil. Not the cheap stuff that they sell in the big box stores that isn't really tung oil, but the real stuff from http://www.realmilkpaint.com/oil.html here. Mine are almost black, very dark charcoal. It has been over a year since I sealed and they are just now starting to show they need to be sealed again. No big deal, just rub it on with my hand, let it dry over night, and I'm done! If you didn't add charcoal coloring to the concrete to start you might want to try to dark tung oil. I would recomend calling these people and talking to the guy that runs it. He knows a lot. Very helpful.
The nice thing about the tung oil is they still feel like concrete, not plastic, which is what we wanted.
S

My last kitchen (destroyed by a slab leak in July)had concrete counters. THe chocolate brown stain was mixed in the concreted. We did not seal the counters, but buffed them with beeswax every few months. My master bath has green concrete with apricot swirls--again color was mixed in the concrete. In six years I have never had to buff those out.

Can't advise you on topical stains, I always use integral pigment for coloring.

For sealing though, Sealers Choice by AquaMix is my first choice. Food-grade penetrating sealer. Three coats, you can do all three in an hour or so.

Follow that with wax. Renew the wax as needed, usually 6-8 months.

I would love to see pictures! I have always dreamed of doing concrete. But, cost wise we'll have to see if it falls into the budget. Thanks for the tips - I'll keep it in mind if we go forward.