A key is an item that Chip can use to open a lock of the same color. Each key can only be used to open one lock, after which it disappears, with the exception of the green key, which can be used an infinite number of times. Note that more than one key of the same color may be collected, which can then be used to open that many locks.
Keys come in four colors:
The key is a transparent acting floor tile, and monsters will not "collect" the key. In Lynx, however, keys work differently: the blue key is erased by monsters and blocks, and the yellow and green keys are monster-acting walls.