My laptop has a yellow USB port. Is it USB 3.0?
A yellow USB port usually denotes an "always on" port. It supplies power to the device plugged into it even when the laptop is off.
It can be whatever colour that your manufacturer wants it to be - I do not think there is a standard.
That being said, every product I have seen that supports USB 3 seems to have a blue socket, so there may be one!
If it is yellow, my guess is that it may be a way to indicate enhanced/increased/special power output.
What model do you have? If you write the model number, I can take a look to be sure.