... then they should not be used.

If it takes me more time/energy/money to get colored wires (plus , making any sense to it, mark the colors in the drawing) than to wire it up with that grey wire I have kilometres laying around here plus debug the errors resulting from that (some of which I would have been done anyway even if using colored wires), then I'd never go for the colors.

Plus, I have a FREEDOM of making any mixture of it - wire the most of the circuits in grey and use a few colors only for the most important connections.

Or, maybe, use sometimes gray instead of grey? :-)

JW

PS. Extensive coloring might get confusing, too, especially if the colors deteriorate over time. Have you ever had the joy of distinguishing white/light yellow/white with light yellow strips/light yellow with white strips wires? :-)