Don't know about color coding on a boat, but many a/c batteries (nicads) use multiple cells connected in series. While these are usually solid bars, they are still marked with a red + on the pos. end. We had an electric
tug that used large 12 volt "house type" batteries, wired in series to give 28 volts. The connectors were black with a red ring around the pos. terminal end. If you use red or orange tape to mark the pos. end it will alert you that it is a "hot" connection. If you're out of tape, use a punch, screwdriver, etc. to punch a + in the terminal lug and drop some paint
in it, assuming you have red paint
I have seen some really crappy wiring jobs, even on aircraft, which are supposed to be "inspected" annually. As a minimum, before undoing a connection, I would mark it with masking tape, and label it. Takes a bit of time, but prevents a lot of "backward" connections.
Remember, Murphy never takes a holiday, and if ya let him, he'll bite ya...