Definitely not a deficiency at this point, more often 2 plants will never be the same shades of green and take a look outside of your grow light because that effects the color as well, just check them under natural lighting, there pretty small at this point and depending on what you're using for soil there's likely enough nutrients in it to get you to the second node, they're very delicate at this point and need maybe a half of shot glass of water as needed but any nutrients could burn them up until they're a bit bigger...