The physical contacts are different though. You can look down into a USB 3 plug and see the new 5 contacts just as you can look at a USB 3 socket and see the new contacts right up front. Also I don't always see blue in new USB 3 cables and sockets, sometimes it's just black.

> Also I don't always see blue in new USB 3 cables and sockets, sometimes it's just black.

True, but if the cable is blue, that always indicates USB 3, at least in my experience—I've never seen a blue USB 2 cable. I think this is sufficient given backwards compatibility—how often do you specifically need a USB 2 device?

I very much doubt many "normal" people know to check the contacts.

Blue or Green if it's a Razer device, or Red to indicate Gen2 vs Gen1 ports on gaming motherboards.

With USB 3 isn’t the other end of the cable usually different as well?

USB-B for USB 3 is physically quite different, yes — looks like two stacked connectors.

It’s a micro usb plus another kind of adapter. This gives you backwards compatibility for devices if you want to expose usb 2 via usb-a -> micro

I was actually thinking about B rather than micro-B, though I guess both my description and your explanation apply either way!