you'll have to clearseal countertops with any process I would think. adding color powder must be done to the entire batch or you'll have variations on color on seperate mixed batches for each countertop. you can also get the powder stain like what's used in stamped concrete that's thrown on top and troweled into wet crete. and you can also add a hardener to the top also. I used to use these products for spraycrete.
Decorative Concrete Coating Decorative Concrete Resurfacing Decorative Concrete Flooring
you won't have any strength without aggregate unless you use that fiberglass strand stuff they add to concrete.