The blue signifies it is a USB 3.0 port, which means that it communicates with other USB 3.0 devices much faster than the older USB 2.0 -- but it is still compatible with 2.0. The main feature is that it is always powered on, even when the computer is turned off. This makes it useful to recharge your phone, etc. I use it on business trips to charge my phone.
Some other facts about USB 3:
- It delivers 0.9 amps of power, instead of the 0.1A on USB 2. This means it will charge devices faster, and can better handle power-hungry peripherals, like DVD burners.
- It is bidirectional because it has twice as many wires, so that data can flow in both directions at the same time; USB 2 is uni-directional.
- Because of the extra wires, USB 3 cables are thicker and so not as flexible as USB 2 cables
- Maximum transmission speed is 4.8Gbps, some 10x faster than USB 2; the catch is that the computer or the peripheral might be able to handle the speed
- The printer-style plug now looks like a T (see figure below).