There are two colors used for the eyes of most 2006-2008 sets. Many have begun to think these eye colors are tiresome. Their official LEGO names are Transparent Neon Green and Transparent Neon Orange, and they are unique in having the distinctive addition of "Neon" in their names. Why is this?
First, let's look at a peculiarity of the Shop-At-Home catalog advertisements for the Av-Matoran and Shadow Matoran sets. The page screams, "Av-Matoran have yellow eyes...!" and "Shadow Matoran have red eyes...!" Funny that they do not embrace their own color names. We'll get to that in a minute. Clearly, on another note, people are wrong to assume that eye color is not a selling point, or that distinctions in eye colors between heroes and villains is not beneficial. At least, this is the view held by LEGO, who through focus group testing and market research has a lot more evidence backing their views than the assumptions of "what makes sense" by amateur critics.
Now, why, if yellow and red are the eye colors LEGO intends to depict with their current eye color preference, do they not merely use transparent red or transparent yellow eyes? The answer lies in that word "neon." If you have sets that date back this far, find transparent red and transparent yellow System windscreens, as featured in classic space sets-- again, seperating good and evil characters and vehicles. Now draw forth the more prolific trans. neon green and trans. neon orange, the latter of which is of the sort featured in Aquasharks and not the same sort featured in Mars Mission. Comparing the two, it should be clear enough that the "neon" colors seem to glow. The others rather take on the appearance of colored glass.
This phenomenon is just as evident in BIONICLE. Construct heads featuring all four colors in question and it should be clear that the neon colors seem to glow more when not focused in direct light.
Now note that transparent neon orange as an eye color has had a special place in villain sets for a very long time. It can be seen in the Rahkshi sets, the transparent neon orange Kraata featured in the Guurahk shoe, Turaga Dume and Ultimate Dume, the Nivawk, Roodaka, the Piraka, CF's Piraka Fusion, Brutaka, and now the Makuta and Shadow Matoran. Even the Tridax pods are depicted in the glowy evilness of trans. neon orange. Others may not remember it as such, but I always found images of the Roodaka set more striking than images of the Sidorak set, and eye color played a major role.
Ironically, the eye color trend seemed to be reversed in the movies, where yellow-green eyes were featured on Rahkshi and Vahki, and even more notably the "turned" Toa Vakama Hordika. Red-orange eyes found welcome in most hero characters, with the exception of many Ga- and Ko-Matoran who featured blue eyes. It is worthy of note that transparent blue of the variety featured on Kohrak or Toa Nuju might also suffice as a vivid eye color, but with the clear benefit to be had in distinctifying good and evil in sets LEGO might have deemed it in their best interest to go "all the way," rather than leaving such a middle ground.
So I hope people now understand why LEGO offers us what would seem to be cliche and meaningless color schemes. These color schemes depict two of the most bright eye colors in BIONICLE, as well as two of the most vivid colors of transparent LEGO pieces. Merry Christmas, everyone.
With all due respect,
Aanchir: Rachira of Time