First, you double posted this question. Please delete the other one. I do not know if there is a way to fix this problem. I do know that the contractor who did the work should not have scheduled a pour when rain was forecast. They also should have better figured how much concrete was needed so the second truck was there for the other half of the pour. Uneven surface and a bad texturing suggest a lack of experience. You did not get the fix you were promised. You may have to contact a lawyer to give your complaint some teeth. I'm sure you do not want to pay more money to get the job done right, but sometimes there is no choice. This answe should bump your question to the top of list again, so perhaps someone with more concrete experience can explain what can be done to fix this.

Parents had a slab done, not stamped however. They wanted a brownish/ rusty kind of color. Color was added to cement mix, not applied color. It looked pinkish after it was poured. Cement guy said it will darken up after sealant. Had to wait to seal the next summer. A clear sealer made it much darker and pretty much the color they were hoping for. We were actually quite surprised, really didn't believe the cement guys that the color would change so much. Talk to your contractor. But the texture does look off possibly. It's really quite a art to get it right. FYI, have seen alot of fancy custom concrete over the past 10 years or so, at a association my parents belong to, at least 30 custom concrete slabs. New association started 15 years ago. Some of it pretty amazing work, some not. Rumor was one guy paid about $8,000 for his 36' x 8' concrete work, looked like wide plank wood boards. One poor guy ended up with a poor job. It was poured and stamped on a really hot day (around 100). Concrete was setting up too fast (also didn't wet down the surface it was being poured on) wasn't floated properly, was setting up when trying to stamp. It was done by inexperienced guys (owner always tried to get cheapest bid) He was too cheap to have it done over by experienced guys. Basically negotiated with concrete guys afterwards and paid hardly anything.

Rain the day after is not usually an issue (not great to pour DURING rain though as it can effect the mix). It actually prevents the concrete from drying out too fast. I have seen people watering their concrete the day or two after it was poured in the summer to avoid it drying too fast. I had a driveway poured three weeks ago and believe me I was so nervous about the weather when it was poured as we had just had a few hot days, but day it was poured was a bit more moderate and we got some rain next day (and I was very happy). Don't hold me to this as I am not a concrete pro, but I am familiar with concrete driveways and such. This looks like efflorescence. Concrete takes time to cure. As it cures, salts come to the surface (the salts would be whatever was in the water, sand, or gravel that is in the mix) and show as white spots like this. If this is indeed it, it does not affect strength or anything, it is aesthetics only. I have some of these showing up too. If it has been a couple months since it was poured, you can remove them with a concrete efflorescence cleaner. As for sealing...if you "must" depends on your climate and how your municipality deals with winter. Where I am we are told to seal every fall with a penetrating concrete sealer as the salt/sand mix used by the City for the roads is brutal on concrete. We are actually required to in order to maintain our warranty. Really, I would do it anyway as it does lengthen the life of it :)

"somehow he was rated an “A” on Angie’s List" It's easy to get an A there. Just buy their advertising. They'll quietly make your "unjustified" negative reviews go away. I'm not just blowing smoke here. I was one of their users, back in the days when you had to pay, and I had my negative reviews deleted. BTW, when I used AL to choose contractors, I had about a 50% success rate. That is, roughly half were really good, and roughly half were pretty awful. I do about as well now by picking people from the local newspaper classified ads and checking them out with the BBB. The other problem with AL (and probably most contractor review services) is that many homeowners don't have a clue how good a job they've gotten. The vast majority of the AL reviewers wrote about whether the workers arrived on time, spoke politely, didn't play loud music or smoke or swear, cleaned up after themselves, and never ever asked to use the bathroom.