If you are talking about the GFCI, which I would never run a tank without, there are two kinds: non-resetting and self-resetting. Non-resetting is by far the most common as it is used any time someone is doing construction work.
The non-resetting units are almost always yellow but can be other colors. A non-resetting unit is not good for use on aquariums because if the power shuts off, like from a power failure, the unit does not turn back on by itself when power is restored. If you think about it, on a construction site you don't want a saw suddenly turning back on.
The self-resetting units are good for an aquarium because they do reset when the power comes back on, power washers are a common user of self-resetting GFCIs. They can be any color but black or yellow are most common.
Neither unit will automatically reset from a ground fault (circuit trip) that would be a very bad idea.
A grounding probe is just a rod, usually titanium, that is connected to a ground circuit, most commonly at the wall outlet. It is designed to be the least resistant path to ground for stray voltages. It will prevent you from getting shocks from your tank but it does not replace a GFCI which is your first and best line of defense.
Ideally you have both on your tank. It is cheap insurance.