Except there not even in the same place depending on the area...
Some are red on top green on bottom and I've also seen red on the left and green on the right, i've also seen left turn green on the left, red, yellow, green, right turn green on the right.
Some places have the lights directly overhead, some place them off to the side of the road, some are in the middle of the intersection suspended by crossed wires...
I have traveled extensively inside the USA and have never seen one such occurence.
I haven't traveled very extensively at all and have seen all of the above... perhaps you're not paying very close attention? Back to the main point though, I wouldn't exactly call them blue (the ones I've seen anyway) they are just not the same primary green your accustomed too and are more of a teal color.