Weapons have different graphics, skins. The fiery swords are 'fiery dragon swords', you need to get one of these types of weapons if you want a different look.
You can dye your weapons, the colours are hardly noticable on some, but some weapons can see the change in dye colours very obvious.
EDIT: Oh yes, I remember one ranger had a nice half-moon. All half-moon I see are normal. But his was glowing with lightning aura. Defenitely I saw lightning aura. And that player himself said that the bow was lightning damage. Anyone else can confirm this??
i am not sure we are talking of the same thing...i mean cool fire burning weaps...not a plain dyed weapon...have you done quest in desert where you must kill your clone...? he has a kick ass weapon skin
Ok, you can change the apperance of a weapon just by adding a mod to it, that just changes the stats of it. And the "Icy" weapon that your doppleganger uses is only for him, i have never seen it anywhere else. And the "Lightning Bow" that you were talking about, its called a storm bow, its a transparent blue color with blue "lightning" circles going up the bow. And like they said earlier, you can change the color of the weapon. That is the only thing you can do to it that will change its apperance. If you really want a cooler looking weapon, save up your cash and buy something valuable.