I had always assumed that when you buy fuel for your road vehicle, the fuel nozzle you insert makes metal to metal contact before any fuel flows. Presumably to prevent static discharge, which reduces the likelihood of an exciting day out. The fuel hose presumably has a secure and mandated internal wiring
pathway to the fuel bowser earth.
So one would hope/expect the same thing for a boat. However! The fuel delivery
company can't always be sure that there is an electrical
connection to the tank and I have seen a fuel delivery
company supply and use their own cable connection.
Also, many boats have long non metalic fuel hoses from the deck inlet to the tank and fuel flowing along these hoses may be prone to static charge build up during rapid fuel flow. Large diameter fuel hoses that meet safety
standards do actually have internal metal spiral wires, but this is not a guarantee that the wires make contact with metal fittings at both ends. (Not applicable to outboard
So if that red cable shown does not make it to the metal deck fitted fuel inlet, I would ensure that problem was addressed. Frankly, the colour is irrelevant, but the colour choice might have been the installer trying to imply that the cable is not an "earthing" connection (i.e. not connected to the engine negative earth) but rather a special wire for specifically connecting the metal tank to the inlet - although red seems a bit alarming... Maybe earthing a fuel tank might make it a "target" during a lightening strike?
The position becomes further blurred if the fuel tank is nonmetallic as many now are.
Fire outbreaks at fueling outlets are not uncommon so a thorough check might be in order. Ask your friendly local fuel delivery company what they expect/prefer. I asked around locally and the general comment was that it was not all that relevant on small boats - which wasn't much help at all.