Yellow: Deep Cycling. Designed with audio or other demanding applications in mind
Blue: same as yellow but different style terminals
Red: Non deep cycling. Designed as a starter battery and a replacement for regular applications
Orange: same as red but positive and negative terminals locations are reversed.
If you have audio equipment or plan get some in the near future, get a Yellow top. Otherwise, get an orange top. The reason I suggest getting an Orange top is because in most cases the stock wires won't reach the terminals found on the red tops. The only downside is that the orange top may be hard to come by and most stores don't know they exist let alone sell them. If you decide to go with any other battery other than the orange and need to extend your wires, checkout my tutorial - http://www.toyotanation.com/forum/t40482.html
All the specs of the batteries are on Optima's site