well you can't get purple if you're republic, and can't get cyan if you're empire for starts. What about white crystals? torhead has them so everyone in the game must have them right?
The point people are trying to get you to see is that there are a very limited number of colors available to players in the first place, and then some of these are restricted either by faction or light/dark alignment.
So if you're a darkside empire player you can only chose from red, orange, yellow, purple, red-black, magenta; with the last 3 being hard to obtain and only for max level.
(afaik)
edit: you can also get yellow-black (level 7 only), and green-black (level 5(?) only and have to purchase an overpriced razer product).