You can get orange gear as rewards, drops or from the Cartel Market or GTN. While you could go through PVE game just using the green/blue stuff that drops, Orange allows you to change the stats with mods, etc. when you need to. Another benefit is you can get the look you want and never have to change it as long as you keep updating the mods. If your going to do endgame stuff and PVP, orange is a must because you will find yourself underpowered/outmatched without it.