Sorry for late reply but the "newer"
Marine 12v wiring color "codes" often use Yellow for Neg/12v-
The newer wire color is especially common in paired conducter "cord" that has yellow and red together with red being +.
With the exception of memory wires there are few yellows that are pos. but watch out for the yellow with red stripe(start solenoid).
12v neg uses black, yellow, and sometimes green that ive seen.
green is often the bonding circuit wire and when connected to rails and frames it can be part fo a lightning static diversion system that
prevents secondary strike paths from forming by bleeding off static.
theya re putting a yellow stripe on some of it now.
some bonding wires are also bare or black.
i guess i should check current nmma and related org updated codes. here is some basic
info , engine wirine and dash wiring are often separate but of course they often tie in and gray wire that is normally nav lights turns up everywhere on elec accessories -- just like red and black.
http://www.marinco.com/page/marinecolorcodeswe will likely see in the future--- red for unswitched pos, yellow for most neg,and separate colors for each Traditional item pos after their switch or fuse.
its a good idea to tag wires that may confuse.