They have a crystal that can be removed. You can use the weapon if your darkside, even though it has a blue crystal. If you remove the crystal it then takes on the Lightside restriction and thus it is worthless to darkside. It was something I noticed after seeing weapon after weapon drop and they all were Blue crystals. Again this is only really concerning the majority of the new 1.1 items.

The new weapons introduced in 1.1 have the best crystals available in the game, with stats of 41 endurance, power or critical rating. These weapons themselves do not have any light or dark restrictions. However, all the crystals are blue. So if you are light side, you are free to remove the crystal and place it into any other weapon you desire, making it very easy to get what you need. If you are dark side, you are forced to find the specific weapon with the specific type of crystal for your current build. Normally, there are mirror versions of weapons for light and dark, with the same stats. This does not seem to be the case with these new set of items. I can only assume there is a bug where the crystals were not designed to be removable or there was an omission for a set with Red crystals. Either way, the current situation goes against the concept that choices for Light and Dark will not give you a game advantage.