I need to top off my antifreeze/coolant on my 09 G37, it currently has green coolant but it's low, so before adding anything to it, I'm looking for advice from anyone with knowledge and experience that can direct me as to what kind would be best to add to it without having to completely drain and replace it.

You can use blue when you replace it or for topping off, blue is simply an "extended service" version of green rated for 5 years instead of 3. They're completely miscible and interchangeable. Don't use any other colors. In particular, never mix either one with orange.
Orange + green/blue = jello.

VStar650CL- Do you know if there is any difference between the blue Zerex 50/50 for Asian vehicles, and the (LLC) NISSAN blue 50/50?

There's no meaningful difference that I know about, the "Asian Green" and "Asian Blue" are all POAT types in use by Honda, Mazda, Hyundai, and Nissan since about 1996. Toyota's is also a POAT type but red in color, my understanding is that it's miscible despite that. Pink, purple, and European blue are all OAT, SOAT, and SHOAT types that shouldn't be used in a Nissan but I think would probably damage it slowly. Like I said, orange (Dex-Cool) is the one that will cause catastrophic damage when mixed with POAT. It's Potassium-doped instead of the Phosphate in POAT, and the reaction literally causes a gel to form which will quickly clot the whole system.