One of the technicians I work with is colour blind, luckily the forklifts we look after use number codes every few inches on the wires.

Wires are either all black, grey or white.

Colour coded wiring doesnt really work on plant / machinery / car's etc.

I only have to look at my own car to see the same wire change colour several times as it passes through various connector plugs, so you have to use the number codes printed on them.

Color on wiring? Usually always black. Every make of truck is different. You need a magnifying glass to see any numbers. You are luckey if the last tech put the wires on in the right spot!