T&T: Diesel Filler Cap vs Water Filler Cap - Color or Wrench Type

[Pete Balkus]

After reading the post from the person who accidentally put water in their
fuel, I have the same concern since our Water and Fuel Caps are within a
foot of each other on the starboard side.

I am always concerned about such a mistake being made, especially when tired
or we have people on board that want to help.

Yes - our filler caps do have the words Water and Diesel on top however I am
just thinking about how to make them even more fool proof.

With this in mind are there any Diesel Filler Cap or Water Filler Cap
alternatives available that are Colored vs Stainless Steel / Chrome to help
distinguish Water from Diesel?

Another alternative to help distinguish Water from Diesel might be to have a
different wrench/key type on each so a different wrench type would be
required vs same working on both.

Any thoughts on techniques or Cap Alternatives that might be available?

Thanks...

   Pete