I belive those lines represent rate at which affected by FSD space around ship moves in relation to normal space (FSD by lore is similar to Alcubierre drive concepts). Without them, already flimsy scale sence becomes even worse. Im not blaming devs on that, its somewhat physically accurate, at least as much as gameplay-wise possible. If I'm not mistaken, you will see only white around you at ecxatly 1c, and you will see everything in front of you go back in time while moving FTL.