I think it is 2 passes.
Tri Pass- Allows You to go to Rainbow Islands 1, 2 & 3 whenever you want
Rainbow Pass- Allows You to go to Rainbow Islands 4, 5, 6 & 7
Source- http://www.serebii.net/red_green/items.shtml
Tri Pass-
The Tri-Pass is given to the player by Celio when they arrive at Knot Island's Network Center on the ship with Bill. The pass allows the player to travel via the Seagallop Ferry between the first three islands in the Sevii Islands: Knot Island, Boon Island, and Kin Island. It is required by the player to complete the story that is set on the island. During this story, the player can only travel between these three islands. After completion, the player can travel to any one of the three from Vermilion City's port, and back again.
Rainbow Pass-
The Rainbow Pass is given to the player by Celio after being asked for
the Sapphire at One Island. The pass allows the player to travel via
the Seagallop Ferry to the remaining Sevii Islands. Celio will let the
player keep the Rainbow Pass afterwards.
Hope this helps =P
