Yes they look a little yellow. This could be one of 2 things. First they may be slightly overwatered. This suffocates the roots and they can't absorb nutrients properly. It is best to wait until the soil dries out on top and with plants that size don't saturate the soil. Just lightly water around the seedling. Second I don't see whether your medium is soil or soilless. If it a good quality soil then it should have enough nutrients to feed the plants for a few weeks at least. If it is a low quality soil or soilless then you need to add a low dose (1/4 strength) feed to give them the nutrients they need. I really think the watering is the issue in your case. Good luck with your grow!