I have had a fair amount of seedlings show purple like this. A number of people here experience it from what I have read. It usually goes away when they get a bit larger. I wouldnt worry if they aren't larger established plants showing purple striping on the stem.
On another note, 2 weeks from when it broke soil? or when you put it in soil? Looking a bit small. Maybe some more light? Or maybe your light is too far away? Hard to say without more info. But it looks fine otherwise.