Not the best work I've seen. The discoloration is normal. I had a titanium exhaust system made for my Yamaha R1. Each section had the same discoloration at the weld joint, though the welds on that exhaust were far better than those on the OP's bike. The maker asked if I wanted to leave the "oil slick" effect from the welds, or have everything media-blasted. He claimed it made little difference as the exhaust heat would discolor the tubes anyway (he was right). But that work on the OP's frame looks like something an office worker attempted when the welders were out of town. I wouldn't accept that repair.