I installed the red OEM kit in mine and judging by the diagrams in the installation instructions they look the same. It's hard to say for sure though unless you put both side by side.
There are so many red accents in the Si as well as the colors in the display, I'm not sure the blue would look good. I don't remember seeing anyone else who's done it. Maybe you'll be the first.
I'd suggest looking through the different threads talking about the OEM accent lights. There is a small modification that can be done to make the red ones brighter. They don't throw much light right out of the box.
The wiring is the same for both kits as long as you stay within the same model year. The only differences are the LED colors and the supplied lenses.
The red kit comes with red LEDs and blue lenses. The blue kit comes with blue LEDs and clear lenses.
As for how blue would look on an Si, that's just a matter of personal taste.