I think that's too subtle for many consumers and it has been hard for manufacturers to stick to that, especially when selling cords in specific shades of colors is good product differentiation.
It worked for PS/2 keyboards and mice. When Microsoft first introduced PC'97 everyone mocked it, saying that even if the computer had coloured ports you never had a coloured keyboard and mouse or vice versa - but eventually after a few years the standard became established enough. And that standard relied on some truly nasty shades of purple and green.
