I think TKA means the core of a lightsaber. It's always white. If you observe closely it's just white with an edge of the favorite colour. That way, Silver and white blades look just the same. Same goes for a black blade...it would be white with a black edge...which would look strange and not be black at all
Anyways, maybe the game will feature the same unlock system as Need for Speed Most Wanted? That you can pick an lightsaber, force or clothing upgrade after every boss you beat.