There was talk a while back about end level Razer Crystals but as of today's date nothing has happened... So, while the crystals are nice to begin with they rapidly become just cosmetic, rather than being much use. And yes, there's a VERY slight difference in shading to the advanced black-green crystal you can get in game... Not that anyone would notice! :/
Last I've heard, there are vendors at capital planets that should have option to trade in crappy ones for endgame.
the vendor is actually a "mods" vendor, not a crystal vendor... The crystals are right at the bottom of the list, and reguire you to trade in 1 of your old crystals and some credits for the newer version
On Dromund Kaas he is called - Shommox (located in the room behind the skill mentor in Kaas city)
On Coruscant he is called - Dommu (located in the alcove next to the cantina in the senate tower)
Hope this helps