Seedling yellow leaves

Yellowing at this stage is usually over watering or light intensity. Are they outside already? If they are, you may need to filter out their light for a week or so until they're large enough to handle the power of the sun. If theyre indoors, how close to the lights are they? How frequently are you watering and does the top of the soil dry out a little before you water again? Also, what kind of soil are you using. If it's a seed starter mix or similar, it probably doesnt have any nutrients in it as well. Some soils need to be amended with a fertilizer from early on. You would have to check the label. Some say feed after 4 weeks and some say feed immediately or instruct you to mix in fertilizer.