From the Super Mario Wiki
Bananaport Pads, or simply Bananaports, are objects in Donkey Kong 64 that allow easy travel in various areas via "bananaport", a large banana with a zipper. It comes in numbers 1 - 5 and each of the two pairs of Bananaport Pads need to be activated to work. Each Bananaport Pad has a different color depending on what number it has, 1 is blue, 2 is green, 3 is purple, 4 is red and 5 is yellow. In order to use a Bananaport Pad, the player needs to stand on one and press the button to bananaport to the other Pad of the same number. Although each area generally only has one pair of each Bananaport number, some areas have two sets of a few bananaports, generally to make navigating sub-areas easier.