The colors are not without meaning: for example, silver gray represents a shuttle line. The NYC subway has more than one shuttle. I'm not sure they're being used right now, but the shape of a symbol also matters. The default shield shape is a circle but a diagonal indicates a different route. They all convey info but as you said, they're imprecise.

In Boston, colors are used. If you say the Red Line or the Orange Line, first, that's what they're officially called, but there's also no chance of confusion, they're one line with a couple of short spurs.