Are you talking about the color of the lightsaber blade itself, or the colored circle around the lightsaber icon in your HUD? The color of the lightsaber blade is purely cosmetic. The color displayed in your lower right HUD is your saber style. Saber styles do affect gameplay; different styles have different swing speeds, damages, perks, etc.
I'm far from being a good duelist, but yellow is the "jack of all trades" style and is probably the best to start learning Jedi/Sith with. Assuming you're playing open mode, yellow is also proficient at dealing with any enemy gunner with its medium damage and swing speed.I meant the blade, and ohhhh Ok. What's a style you recommend?