mnittler:
I think the color is a matter of personal preference. However, given the choices you presented, I would go with the blue over the black. The darker finishes will keep the pool water warmer than a lighter color surface but that may or may not be what you are going for in South Texas. Another thing to consider is resale. Most people prefer a more traditional lighter color pool surface that has a bluish color to it. While the dark/midnight blue is a dark shade of blue, it would at least have a bluish color that appeals to most people.
The pebble finish will provide a bit more durability over plain plaster at the expense of a slightly rougher surface.