Red is a "starting" type batt, similar to a normal batt, except with optima's they are sealed batts. Normal batts aren't sealed.
Yellow and blue tops are deep cycle batts for audio, RV, marine etc. If your' only going to have one, you should get a deep cycle batt. It does not have to be an optima or sealed batt. Most people now recommend the kinetic. I'd stick with the major batt brands like kinetic or optima.
I have two batts. A red top under the hood and a yellow top in the rear thru a battery isolator. You don't need two batts, I did it so I could listen with the engine off when I go camping.