The posts referring to the colors making different power by the members was in jest. The colors were merely done for asthetic purposes. Some people like the plain silver of the aluminum, some have gone with certain color schemes in their vehicles and like to match things. Really just to make them stand out a bit and be different.
You do have a point though. I could have tested and found differnet amounts of gain and then assigned the thickness/power gains to colors but I didnt. The power gain has been tested and showed definitive gains with the spacer at 1/2 an inch thick. Whether or not it gains or loses with thicker or thinner spacers has not really been tested further once the 1/2 showed the considerable gains that it did on a dyno.
From the oil fill side of the engine you can see the blue spacer on my truck. Its not hugely visible without trying to see it but once you know where to look you can see it. (see pics)
BTW, the dynos were done by a Jaguar mechanic in Texas who is a big source of credible information on the Frontier and Xterra sites.