Thanks so much to the two of you. I used acetone and the magic eraser and scrubbed a lot and it finally came off. Thanks again.

See if you can run a steak knife between the bottom of the stone and the sink flange. If so, your sink is leaking and trapping water there. The stone is sucking up the trapped water. The solution would be to drop the sink, let it dry completely, #40 peroxide (beauty supply store) the crack, superglue the crack with the runny stuff, seal the stone bottom, silicone the sink flange and strap it in place, then seal the top.

Thanks Joseph! I had limited success at first, but eventually with a combination of the Homax caulk removal tool (well built strong/durable so very good for hard strong stiff caulk) and using a blade to score the caulk at the tile line and tub line, I got some of the caulk out. After the above, there was still a lot more caulk as this method worked with limited success (since I found out the caulk was wedged in deeply into gap between the bottom tile and the tub border. But there was one spot where I had managed to get more caulk out. So I took a small watch / computer screw driver (with a blade width as close to the gap between the tile and tub border as possible). I carefully wedged the screw driver blade in that spot and was able to get 'behind' the bead of caulk. Suddenly I was able to extract 3 long INTACT strips of caulk to clear ALL the caulk from the entire width of the tub. Caveat (somewhat obvious) - With Acrylic tubs be careful with using a blade. There is also a caulk tool with teeth that I forgot about till this morning. I will now clean the tub with a PH balanced cleaner and rinse it with water before I apply the new caulk. Note - I decided to remove caulk from one of the 3 sides and not bother with the length and other side given the caulk is more than adequate given the SIGNIFICANT depth of the caulk that I observed between the bottom row of tile and the tub. (The, at first 'apparent', thinness of the caulk is misleading - there is actually a lot of caulk! Also the tub Kohler tub has a lip all around. And the contractor also caulked where the new Durarock backer board meets the new tub. I started this all because just felt that the grout sealant spray had eaten some of the caulk based on how it looked before I used it and after. Anyway, I will caulk this side and see how it turns out before I make a 100% final decision whether to even bother removing NEW caulk on the other two sides.

OK, then get them back to finish the job. If you don't want to do that, then try this: Coat the area with GranQuartz 413 granite sealer or Klean Strip caulk remover. Once this has softened the silicone carefully scrape it off. But, try the solvent first on an area of the countertop not visible (under the countertop edge, for example) to make sure its does not discolor. It's unlikely, but possible. For a scraper, use a single edge razor blade held nearly vertically to the surface. You are not trying to cut it off, you need to scrape it off. If a blade get dull there is a slight risk of scratching the surface. Throw it away and get a new blade. Hope this helps.