Different grades of copper but not for fittings
I noticed there are different types of copper pipe. At least two at the big box stores. I assume the more expensive one is thicker. Called red and blue at HD. Red being the more expensive. But, the fittings, elbows, reducers, etc. are not different grades. Does this mean that I can use them for either grade of pipe? Do they make different grades of fittings that I should be looking for at a plumbing house? Is the pipe at the big box stores any different than the pipe at the plumbing supply houses? I just want to buy the best available for my bathroom remodel and don't want to inter-mix grades if that is bad. Please help. Thanks.