I have just the thing to solve your problem. I had a bird bath,that when new was light bright concrete. I wanted it to look like it was getting Moss covered. Just get some yellowish green(Chartreuse) acrylic paint and some Olive Green acrylic paint, so you can mix to get various shades of green. Dilute the paint with water until it is very liquid. I put mine into an old windex bottle. Then spray the item you want to age from about 2 feet away. the liquid will drip down the side. concrete being porous will soak up the stain. I went back and did several layers with various mixtures. You should start with a very dilute mixture so it light to start with, then add a little more paint to darker the areas you desire. Mine have stayed aged looking for 8 years now. You can also use a sea sponge to dab on the color in spots so it looks like moss starting to grow. You could also use some brownish shades if you want.

I found a way, accidentally. I had a container like a child's swimming pool with water in it. It also had peat moss in it, and my new cement bird bath. When I fished it out after a few days, it had been stained a tea color that I found attractive. I don't know if anyone else has used peat moss. I have also used acrylic paint thinned with water and brushed on and wiped off. This has been good and is permanent. I learned it from an "expensive" cement decor place in Houston.

You must be pretty handy you really did a great job on it. I think in the long run you will be happier with s.s. than porcelain. The latter tends to break things that get dropped in them by accicent. I much prefer to wash veggies from the garden outside as I always reuse that water for plants and that saves carrying it back out. And you dont have to be so careful, who cares if you splash a bit. We have a single burner on the grill and I do a lot of cooking and prep of food around veggie harvest time, outdoors. More room to work, saves messing and heating up the kitchen, and not so far to carry all the scraps. Besides I'd rather be outside, too :) Great job on the sink.

"The holes made to raise the concrete are ugly and the patches are very visible." In my opinion, this is to be expected and is unavoidable. Complete replacement was your only alternative. If your contractor had gotten in before the city, it is likely things would have turned out better. No suggestions about the other issues except to see what he proposes. .