How to find out which USB port is USB 3.0?

They're BLUE!

I believe USB-3 ports should be colored differently (blue)

The use of blue pantone thermoplastics in USB 3.0 connectors is recommended on systems with a mix of USB 2.0 and USB 3.0 ports. For certification, the USB-IF does require that the user be able to clearly and easily distinguish between a USB 3.0 and a USB 2.0 port on a system; however, it is left to the system implementer on how to accomplish this.

(my emphasis)

Also, just because your Computer contains a USB 3 controller doesn't mean it necessarily is presented externally

On my HP laptop, USB 3.0 ports logo/symbol have an "SS" (for Super Speed). USB 2.0 ports only have the typical USB symbol with no "SS".

See the following image:

According the tech specs

Left side: two USB 3.0 ports, external monitor (VGA DB-15, HDMI), ethernet (RJ-45)

Right side: one USB 2.0 port and one eSATA/USB combo port