with the tri-pass you unlock islands 1-3.
with the rainbow pass you unlock islands 4-7
birth island and navel rock and eight and nine islands.
Well here are some of the islands that i have found.Iron Island,fullmoom island,southern island,birth island,navel island.Those are the only islands I've been to.
you have to beat the elite four and then go talk to pro. oak and i think he gives you the pass.
After getting the national pokedex get the ruby and give it to celio. he will give you the rainbow pass for islands 4-7.
After you beat the elite four, get the rainbow pass, and go to islands 4-7. you can catch some on each island.
By defeating the leaders of each colosseum. You'll unlock new battle passes as you progress.
You need to catch more than 60 Pokemon and talk to Oak and get the National Pokedex from him and then go to Island One and talk to the guy near that big weird machine and he'll exchange your tripass for his rainbow pass which allows you to travel to the Sevii Islands (islands 4 - 7) and the first 3 islands.
You get the Rainbow Pass from Bill in order to have access to the other four islands in the sevii islands.
After you have beaten the Elite 4 talk to Oak. If you have caught at least 60 Pokemon he will give you the Rainbow Pass. This will allow you to go to the 7 islands.
rainbow pass
The only "passes" that I can recall from Pokemon FireRed are the Tri-Pass, which grants you access to Islands One, Two, and Three, and the Rainbow Pass, which grants you access to Islands One through Seven (the Sevii Islands).
The Sevii Islands are a fictional archipelago of nine large islands and several small islands surrounding them. They are far south of Kanto, and are home to several legendary Pokemon. They appear in Pokemon LeafGreen and FireRed, and peripherally in Pokemon Emerald.